System and method for compensation of fuel injector limits

ABSTRACT

A method for an engine configured to deliver an actively varying relative ratio of a first and second fuel via a delivery system having a first and second injector for a cylinder of the engine, where the first fuel has a lesser relative amount of alcohol, the method comprising of varying an amount of injection from the first and second injector with operating conditions, when said variation causes said first injector to approach a first minimum opening condition, increasing injection of said second injector and disabling said first injector, and when said variation causes said second injector to approach a second minimum opening condition, avoiding further reduction of said second injector and decreasing injection of said first injector.

BACKGROUND AND SUMMARY

Engines may use various forms of fuel delivery to provide a desiredamount of fuel for combustion in each cylinder. One type of fueldelivery uses a port injector for each cylinder to deliver fuel torespective cylinders. Still another type of fuel delivery uses a directinjector for each cylinder.

Further, engines have also been described using more than one injectorto provide fuel to a single cylinder in an attempt to improve engineperformance. Specifically, in U.S. 2005/0155578 an engine is describedusing a port fuel injector and a direct injector in each cylinder of theengine.

Another approach utilizing multiple injection locations for differentfuel types is described in the papers titled “Calculations of KnockSuppression in Highly Turbocharged Gasoline/Ethanol Engines Using DirectEthanol Injection” and “Direct Injection Ethanol Boosted GasolineEngine: Biofuel Leveraging for Cost Effective Reduction of OilDependence and CO2 Emissions” by Heywood et al. Specifically, theHeywood et al. papers describes directly injecting ethanol to improvecharge cooling effects, while relying on port injected gasoline forproviding the majority of combusted fuel over a drive cycle.

However, the inventors herein have recognized a problem with suchapproaches. For example, a minimum valve opening amount, or minimumpulsewidth, may be encountered when varying injection of one or bothinjectors in response to conditions such as knock sensor feedback duringengine operation, thus generating air-fuel errors.

Thus, in one approach, a method is provided for an engine configured todeliver an actively varying relative ratio of a first and second fuelvia a delivery system having a first and second injector for a cylinderof the engine, where the first fuel has a lesser relative amount ofalcohol. The method comprises varying an amount of injection from thefirst and second injector with operating conditions; and when saidvariation causes said first injector to approach a first minimum openingcondition, increasing injection of said second injector and disablingsaid first injector, and when said variation causes said second injectorto approach a second minimum opening condition, avoiding furtherreduction of said second injector and decreasing injection of said firstinjector.

In this way, it is possible to err on the side of providing extra fuelhaving a greater alcohol content (and thus a greater knock avoidanceeffect. For example, when the first injector approaches as minimumopening, it is disabled so that extra fuel from the second injector canbe used to provide a desired total fuel injection amount. Likewise, whenthe second injector approach as minimum opening, further reduction isavoided so that at least the desired minimum amount of the second fuelis provided, and the first injector may be reduced if necessary toprovide a desired total fuel injection amount.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a vehicle illustrating various componentsof the powertrain system;

FIG. 2 shows a partial engine view;

FIG. 3 shows an engine with a turbocharger;

FIGS. 4-5 show example engine cylinder and port configurations;

FIG. 6 shows two fuel injectors;

FIG. 7 shows a fuel pump system;

FIGS. 8-10 shows fuel vapor purge system configurations;

FIGS. 11-12 shows high level flow charts for air-fuel ratio feedbackcontrol;

FIGS. 13-14 and 16 show high level flow charts for fuel type enablement;

FIG. 15 shows graphs illustrating example ratios of fuel type enablementbased on operating conditions;

FIGS. 16-18 show high level flow charts for engine starting and runningoperation;

FIG. 19 shows a high level flow chart for engine starting taking intoaccount fuel levels of different fuel types;

FIG. 20 shows a high level flow chart for compensating for depleting afuel source;

FIG. 21 shows a graph illustrating different fuel injectorcharacteristics for two example injectors;

FIG. 22 shows a graph illustrating an example relationship of fuelinjection as a function of knock tendency;

FIG. 23 shows a high level flow chart of an alternative embodiment forcontrolling fuel injection of a first and second fuel type taking intoaccount minimum pulse width issues and different fuel typecharacteristics;

FIGS. 24-25 show high level flow charts for controlling operation usingwater injection;

FIGS. 26-27 show graphs illustrating an amount of injection to reduceknock for varying water content and varying amounts of desired chargecooling;

FIG. 28 shows a high level flow chart for controlling fuel typeinjection amounts (and relative amounts) and/or adjusting ignitiontiming to reduce knock;

FIG. 29 shows graphs illustrating example knock control operation;

FIG. 30 shows a high level flow chart for event-based engine starting;

FIGS. 31-34 shows high level flow charts for fuel vapor purging control,estimation, and adaptive learning;

FIG. 35 shows a graph of an example injector characteristic;

FIGS. 36-38 show example fuel tank and pump configurations;

FIG. 39 shows a high level flow chart for transitioning on a second fueltype;

FIG. 40 shows example operation according to the routine of FIG. 39;

FIG. 41 shows a high level flow chart for selecting injection timing(s);

FIG. 42 shows a graph illustrating example injection timing operation;

FIG. 43 shows a graph illustrating fuel types and injection timings forvarious engine speed and load regions; and

FIG. 44 shows a high level flow chart for controlling boost.

DETAILED DESCRIPTION

Referring to FIG. 1, in this example, internal combustion engine 10,further described herein with particular reference to FIGS. 2 and 3, isshown coupled to torque converter 11 via crankshaft 13. Torque converter11 is also coupled to transmission 15 via turbine shaft 17. Torqueconverter 11 has a bypass, or lock-up clutch 14 which can be engaged,disengaged, or partially engaged. When the clutch is either disengagedor partially engaged, the torque converter is said to be in an unlockedstate. The lock-up clutch 14 can be actuated electrically,hydraulically, or electro-hydraulically, for example. The lock-up clutch14 receives a control signal (not shown) from the controller, describedin more detail below. The control signal may be a pulse width modulatedsignal to engage, partially engage, and disengage, the clutch based onengine, vehicle, and/or transmission operating conditions. Turbine shaft17 is also known as transmission input shaft. Transmission 15 comprisesan electronically controlled transmission with a plurality of selectablediscrete gear ratios. Transmission 15 also comprises various othergears, such as, for example, a final drive ratio (not shown).Transmission 15 is also coupled to tire 19 via axle 21. Tire 19interfaces the vehicle (not shown) to the road 23. Note that in oneexample embodiment, this powertrain is coupled in a passenger vehiclethat travels on the road.

In an alternative embodiment, a manual transmission operated by a driverwith a clutch may be used. Further, various types of automatictransmissions may be used.

FIG. 2 shows one cylinder of a multi-cylinder engine, as well as theintake and exhaust path connected to that cylinder. In the embodimentshown in FIG. 2, engine 10 is capable of using two different fuels,and/or two different injectors in one example. For example, engine 10may use gasoline and an alcohol containing fuel such as ethanol,methanol, a mixture of gasoline and ethanol (e.g., E85 which isapproximately 85% ethanol and 15% gasoline), a mixture of gasoline andmethanol (e.g., M85 which is approximately 85% methanol and 15% gas),etc. In another example, two fuel systems are used, but each uses thesame fuel, such as gasoline. In still another embodiment, a singleinjector (such as a direct injector) may be used to inject a mixture ofgasoline and such an alcohol based fuel, where the ratio of the two fuelquantities in the mixture may be adjusted by controller 12 via a mixingvalve, for example. In still another example, two different injectorsfor each cylinder are used, such as port and direct injectors. In evenanother embodiment, different sized injectors, in addition to differentlocations and different fuels, may be used.

As will be described in more detail below, various advantageous resultsmay be obtained by various of the above systems. For example, when usingboth gasoline and a fuel having alcohol (e.g., ethanol), it may bepossible to adjust the relative amounts of the fuels to take advantageof the increased charge cooling of alcohol fuels (e.g., via directinjection) to reduce the tendency of knock. This phenomenon, combinedwith increased compression ratio, and/or boosting and/or enginedownsizing, can then be used to obtain large fuel economy benefits (byreducing the knock limitations on the engine).

FIG. 2 shows one example fuel system with two fuel injectors percylinder, for at least one cylinder. Further, each cylinder may have twofuel injectors. The two injectors may be configured in variouslocations, such as two port injectors, one port injector and one directinjector (as shown in FIG. 2), or others.

Also, as described herein, there are various configurations of thecylinders, fuel injectors, and exhaust system, as well as variousconfiguration for the fuel vapor purging system and exhaust gas oxygensensor locations.

Continuing with FIG. 2, it shows a dual injection system, where engine10 has both direct and port fuel injection, as well as spark ignition.Internal combustion engine 10, comprising a plurality of combustionchambers, is controlled by electronic engine controller 12. Combustionchamber 30 of engine 10 is shown including combustion chamber walls 32with piston 36 positioned therein and connected to crankshaft 40. Astarter motor (not shown) may be coupled to crankshaft 40 via a flywheel(not shown), or alternatively direct engine starting may be used.

In one particular example, piston 36 may include a recess or bowl (notshown) to help in forming stratified charges of air and fuel, ifdesired. However, in an alternative embodiment, a flat piston may beused.

Combustion chamber, or cylinder, 30 is shown communicating with intakemanifold 44 and exhaust manifold 48 via respective intake valves 52 aand 52 b (not shown), and exhaust valves 54 a and 54 b (not shown).Thus, while four valves per cylinder may be used, in another example, asingle intake and single exhaust valve per cylinder may also be used. Instill another example, two intake valves and one exhaust valve percylinder may be used.

Combustion chamber 30 can have a compression ratio, which is the ratioof volumes when piston 36 is at bottom center to top center. In oneexample, the compression ratio may be approximately 9:1. However, insome examples where different fuels are used, the compression ratio maybe increased. For example, it may be between 10:1 and 11:1 or 11:1 and12:1, or greater.

Fuel injector 66A is shown directly coupled to combustion chamber 30 fordelivering injected fuel directly therein in proportion to the pulsewidth of signal dfpw received from controller 12 via electronic driver68. While FIG. 2 shows injector 66A as a side injector, it may also belocated overhead of the piston, such as near the position of spark plug92. Such a position may improve mixing and combustion due to the lowervolatility of some alcohol based fuels. Alternatively, the injector maybe located overhead and near the intake valve to improve mixing.

Fuel may be delivered to fuel injector 66A by a high pressure fuelsystem (not shown) including a fuel tank, fuel pumps, and a fuel rail.Alternatively, fuel may be delivered by a single stage fuel pump atlower pressure, in which case the timing of the direct fuel injectionmay be more limited during the compression stroke than if a highpressure fuel system is used. Further, while not shown, the fuel tank(or tanks) may (each) have a pressure transducer providing a signal tocontroller 12.

Fuel injector 66B is shown coupled to intake manifold 44, rather thandirectly to cylinder 30. Fuel injector 66B delivers injected fuel inproportion to the pulse width of signal pfpw received from controller 12via electronic driver 68. Note that a single driver 68 may be used forboth fuel injection systems, or multiple drivers may be used. Fuelsystem 164 is also shown in schematic form delivering vapors to intakemanifold 44. Various fuel systems and fuel vapor purge systems may beused, such as those described below herein with regard to FIGS. 8-10,for example.

Intake manifold 44 is shown communicating with throttle body 58 viathrottle plate 62. In this particular example, throttle plate 62 iscoupled to electric motor 94 so that the position of elliptical throttleplate 62 is controlled by controller 12 via electric motor 94. Thisconfiguration may be referred to as electronic throttle control (ETC),which can also be utilized during idle speed control. In an alternativeembodiment (not shown), a bypass air passageway is arranged in parallelwith throttle plate 62 to control inducted airflow during idle speedcontrol via an idle control by-pass valve positioned within the airpassageway.

Exhaust gas sensor 76 is shown coupled to exhaust manifold 48 upstreamof catalytic converter 70 (where sensor 76 can correspond to variousdifferent sensors). For example, sensor 76 may be any of many knownsensors for providing an indication of exhaust gas air/fuel ratio suchas a linear oxygen sensor, a UEGO, a two-state oxygen sensor, an EGO, aHEGO, or an HC or CO sensor. In this particular example, sensor 76 is atwo-state oxygen sensor that provides signal EGO to controller 12 whichconverts signal EGO into two-state signal EGOS. A high voltage state ofsignal EGOS indicates exhaust gases are rich of stoichiometry and a lowvoltage state of signal EGOS indicates exhaust gases are lean ofstoichiometry. Signal EGOS may be used to advantage during feedbackair/fuel control to maintain average air/fuel at stoichiometry during astoichiometric homogeneous mode of operation. Further details ofair-fuel ratio control are included herein.

Distributorless ignition system 88 provides ignition spark to combustionchamber 30 via spark plug 92 in response to spark advance signal SA fromcontroller 12.

Controller 12 may cause combustion chamber 30 to operate in a variety ofcombustion modes, including a homogeneous air/fuel mode and a stratifiedair/fuel mode by controlling injection timing, injection amounts, spraypatterns, etc. Further, combined stratified and homogenous mixtures maybe formed in the chamber. In one example, stratified layers may beformed by operating injector 66A during a compression stroke. In anotherexample, a homogenous mixture may be formed by operating one or both ofinjectors 66A and 66B during an intake stroke (which may be open valveinjection). In yet another example, a homogenous mixture may be formedby operating one or both of injectors 66A and 66B before an intakestroke (which may be closed valve injection). In still other examples,multiple injections from one or both of injectors 66A and 66B may beused during one or more strokes (e.g., intake, compression, exhaust,etc.). Even further examples may be where different injection timingsand mixture formations are used under different conditions, as describedbelow.

Controller 12 can control the amount of fuel delivered by fuel injectors66A and 66B so that the homogeneous, stratified, or combinedhomogenous/stratified air/fuel mixture in chamber 30 can be selected tobe at stoichiometry, a value rich of stoichiometry, or a value lean ofstoichiometry.

Emission control device 72 is shown positioned downstream of catalyticconverter 70. Emission control device 72 may be a three-way catalyst ora NOx trap, or combinations thereof.

Controller 12 is shown as a microcomputer, including microprocessor unit102, input/output ports 104, an electronic storage medium for executableprograms and calibration values shown as read only memory chip 106 inthis particular example, random access memory 108, keep alive memory110, and a conventional data bus. Controller 12 is shown receivingvarious signals from sensors coupled to engine 10, in addition to thosesignals previously discussed, including measurement of inducted mass airflow (MAF) from mass air flow sensor 100 coupled to throttle body 58;engine coolant temperature (ECT) from temperature sensor 112 coupled tocooling sleeve 114; a profile ignition pickup signal (PIP) from Halleffect sensor 118 coupled to crankshaft 40; and throttle position TPfrom throttle position sensor 120; absolute Manifold Pressure Signal MAPfrom sensor 122; an indication of knock from knock sensor 182; and anindication of absolute or relative ambient humidity from sensor 180.Engine speed signal RPM is generated by controller 12 from signal PIP ina conventional manner and manifold pressure signal MAP from a manifoldpressure sensor provides an indication of vacuum, or pressure, in theintake manifold. During stoichiometric operation, this sensor can givean indication of engine load. Further, this sensor, along with enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In a one example, sensor 118, which is also used as anengine speed sensor, produces a predetermined number of equally spacedpulses every revolution of the crankshaft.

In this particular example, temperature Tcat1 of catalytic converter 70is provided by temperature sensor 124 and temperature Tcat2 of emissioncontrol device 72 is provided by temperature sensor 126. In an alternateembodiment, temperature Tcat1 and temperature Tcat2 may be inferred fromengine operation.

Continuing with FIG. 2, a variable camshaft timing system is shown.Specifically, camshaft 130 of engine 10 is shown communicating withrocker arms 132 and 134 for actuating intake valves 52 a, 52 b andexhaust valves 54 a, 54 b. Camshaft 130 is directly coupled to housing136. Housing 136 forms a toothed wheel having a plurality of teeth 138.Housing 136 is hydraulically coupled to crankshaft 40 via a timing chainor belt (not shown). Therefore, housing 136 and camshaft 130 rotate at aspeed substantially equivalent to the crankshaft. However, bymanipulation of the hydraulic coupling as will be described laterherein, the relative position of camshaft 130 to crankshaft 40 can bevaried by hydraulic pressures in advance chamber 142 and retard chamber144. By allowing high pressure hydraulic fluid to enter advance chamber142, the relative relationship between camshaft 130 and crankshaft 40 isadvanced. Thus, intake valves 52 a, 52 b and exhaust valves 54 a, 54 bopen and close at a time earlier than normal relative to crankshaft 40.Similarly, by allowing high pressure hydraulic fluid to enter retardchamber 144, the relative relationship between camshaft 130 andcrankshaft 40 is retarded. Thus, intake valves 52 a, 52 b, and exhaustvalves 54 a, 54 b open and close at a time later than normal relative tocrankshaft 40.

While this example shows a system in which the intake and exhaust valvetiming are controlled concurrently, variable intake cam timing, variableexhaust cam timing, dual independent variable cam timing, or fixed camtiming may be used. Further, variable valve lift may also be used.Further, camshaft profile switching may be used to provide different camprofiles under different operating conditions. Further still, thevalvetrain may be roller finger follower, direct acting mechanicalbucket, electromechanical, electrohydraulic, or other alternatives torocker arms.

Continuing with the variable cam timing system, teeth 138, being coupledto housing 136 and camshaft 130, allow for measurement of relative camposition via cam timing sensor 150 providing signal VCT to controller12. Teeth 1, 2, 3, and 4 are preferably used for measurement of camtiming and are equally spaced (for example, in a V-8 dual bank engine,spaced 90 degrees apart from one another) while tooth 5 is preferablyused for cylinder identification, as described later herein. Inaddition, controller 12 sends control signals (LACT, RACT) toconventional solenoid valves (not shown) to control the flow ofhydraulic fluid either into advance chamber 142, retard chamber 144, orneither.

Relative cam timing can be measured in a variety of ways. In generalterms, the time, or rotation angle, between the rising edge of the PIPsignal and receiving a signal from one of the plurality of teeth 138 onhousing 136 gives a measure of the relative cam timing. For theparticular example of a V-8 engine, with two cylinder banks and afive-toothed wheel, a measure of cam timing for a particular bank isreceived four times per revolution, with the extra signal used forcylinder identification.

Sensor 160 may also provide an indication of oxygen concentration in theexhaust gas via signal 162, which provides controller 12 a voltageindicative of the O2 concentration. For example, sensor 160 can be aHEGO, UEGO, EGO, or other type of exhaust gas sensor. Also note that, asdescribed above with regard to sensor 76, sensor 160 can correspond tovarious different sensors.

As described above, FIG. 2 merely shows one cylinder of a multi-cylinderengine, and that each cylinder has its own set of intake/exhaust valves,fuel injectors, spark plugs, etc.

Also, in the example embodiments described herein, the engine may becoupled to a starter motor (not shown) for starting the engine. Thestarter motor may be powered when the driver turns a key in the ignitionswitch on the steering column, for example. The starter is disengagedafter engine starting, for example, by engine 10 reaching apredetermined speed after a predetermined time. Further, in thedisclosed embodiments, an exhaust gas recirculation (EGR) system may beused to route a desired portion of exhaust gas from exhaust manifold 48to intake manifold 44 via an EGR valve (not shown). Alternatively, aportion of combustion gases may be retained in the combustion chambersby controlling exhaust valve timing.

As noted above, engine 10 may operate in various modes, including leanoperation, rich operation, and “near stoichiometric” operation. “Nearstoichiometric” operation can refer to oscillatory operation around thestoichiometric air fuel ratio. Typically, this oscillatory operation isgoverned by feedback from exhaust gas oxygen sensors. In this nearstoichiometric operating mode, the engine may be operated withinapproximately one air-fuel ratio of the stoichiometric air-fuel ratio.This oscillatory operation is typically on the order of 1 Hz, but canvary faster and slower than 1 Hz. Further, the amplitude of theoscillations are typically within 1 a/f ratio of stoichiometry, but canbe greater than 1 a/f ratio under various operating conditions. Notethat this oscillation does not have to be symmetrical in amplitude ortime. Further note that an air-fuel bias can be included, where the biasis adjusted slightly lean, or rich, of stoichiometry (e.g., within 1 a/fratio of stoichiometry). Also note that this bias and the lean and richoscillations can be governed by an estimate of the amount of oxygenstored in upstream and/or downstream three way catalysts.

As described below, feedback air-fuel ratio control is used forproviding the near stoichiometric operation. Further, feedback fromexhaust gas oxygen sensors can be used for controlling air-fuel ratioduring lean and during rich operation. In particular, a switching type,heated exhaust gas oxygen sensor (HEGO) can be used for stoichiometricair-fuel ratio control by controlling fuel injected (or additional airvia throttle or VCT) based on feedback from the HEGO sensor and thedesired air-fuel ratio. Further, a UEGO sensor (which provides asubstantially linear output versus exhaust air-fuel ratio) can be usedfor controlling air-fuel ratio during lean, rich, and stoichiometricoperation. In this case, fuel injection (or additional air via throttleor VCT) can be adjusted based on a desired air-fuel ratio and theair-fuel ratio from the sensor. Further still, individual cylinderair-fuel ratio control could be used, if desired. As described in moredetail below, adjustments may be made with injector 66A, 66B, orcombinations therefore depending on various factors.

Also note that various methods can be used to maintain the desiredtorque such as, for example, adjusting ignition timing, throttleposition, variable cam timing position, exhaust gas recirculationamount, and number of cylinders carrying out combustion. Further, thesevariables can be individually adjusted for each cylinder to maintaincylinder balance among all the cylinders.

Referring now to FIG. 3, an example engine 10 is shown with four in-linecylinders. In one embodiment, engine 10 may have a turbocharger 319,which has a turbine 319 a coupled in the exhaust manifold 48 and acompressor 319 b coupled in the intake manifold 44. While FIG. 3 doesnot show an intercooler, one may optionally be used. Turbine 319 a istypically coupled to compressor 319 b via a drive shaft 315. Varioustypes of turbochargers and arrangements may be used. For example, avariable geometry turbocharger (VGT) may be used where the geometry ofthe turbine and/or compressor may be varied during engine operation bycontroller 12. Alternately, or in addition, a variable nozzleturbocharger (VNT) may be used when a variable area nozzle is placedupstream and/or downstream of the turbine in the exhaust line (and/orupstream or downstream of the compressor in the intake line) for varyingthe effective expansion or compression of gasses through theturbocharger. Still other approaches may be used for varying expansionin the exhaust, such as a waste gate valve. FIG. 3 shows an examplebypass valve 320 around turbine 319 a and an example bypass valve 322around compressor 319 b, where each valve may be controller viacontroller 12. As noted above, the valves may be located within theturbine or compressor, or may be a variable nozzle.

Also, a twin turbocharger arrangement, and/or a sequential turbochargerarrangement, may be used if desired. In the case of multiple adjustableturbocharger and/or stages, it may be desirable to vary a relativeamount of expansion though the turbocharger, depending on operatingconditions (e.g. manifold pressure, airflow, engine speed, etc.).Further, a supercharger may be used, if desired.

Referring now to FIG. 4, an alternative embodiment of engine 10 is shownwith two port fuel injectors per cylinder for cylinders with three ormore valves (e.g., two or more intake valves, such as a 3-valve engineor a 4-valve engine). Even though this example utilizes port injection,it may still be possible to exploit increased charge cooling effects ofvarious fuels (such as ethanol, gasoline, mixtures thereof, etc). Forexample, in some cases, port injection can attain some charge coolingbenefits at wide-open throttle conditions by using open valve injection(OVI). However, since an additional injector is supplied, the wide-openthrottle OVI benefit may not be reduced by the need to design singleport-injector systems to satisfy other constraints, such as: control atlow fuel flows, cold start fuel behavior, and transient fuel behavior(usually with closed-valve injection). Thus, by using two fuel injectorsit is possible to better exploit open valve injection, while stillretaining desired functionality during various operating conditions.

As one example, since two injectors are used, they may each be designedwith smaller valve flows/openings so that under low load conditions itmay be possible to provide more accurate quantity control (e.g., byusing only one of the injectors).

As another example, when using different fuels for two the injectors(e.g., one injecting gasoline and one injecting a fuel having an alcoholcomponent, such as ethanol or E85) many of the above system constraintscan be satisfied. For example, by using separate port injectors forfuels with alcohol (e.g., ethanol) and gasoline, and using the alcoholinjector at higher loads when the engine is warmed up, some of theconstraints at low fuel flow and cold start are avoided for the alcoholinjector. Further, if the alcohol injector is operated with OVI timing,or at least partial OVI timing, then transient fuel problems may also bereduced for the ethanol injector.

Additionally, using OVI timing (at least under some conditions) allowsthe alcohol injector spray pattern and targeting to be optimized forOVI. The spray could be much narrower angle than for the gasoline portinjector, to increase the probability that most of the fuel enters thecylinder as a liquid, instead of evaporating from intake port and intakevalve metal surfaces. This would increase the evaporative coolingbenefit in a manner similar to direct injection. Also, the injectortargeting may be selected to reduce bore wash issues, in which liquidfuel washes oil off cylinder walls, potentially causing excessive wear.

In this way, in some cases, it may be possible to achieve advantageousresults without requiring direct injection. For example, by using twoport fuel injectors per cylinder it may be possible to reduce systemcost, reduce required fuel rail pressure (high fuel rail pressure canreduce fuel economy due to parasitic losses of the fuel pump), andreduce packaging issues (direct injection may require compromised valvesizes and/or angles, intake or exhaust port shapes, etc.).

Specifically, FIG. 4 shows a cylinder 430 with two intake ports 446 aand 446 b of intake manifold 444 coupled respectively to intake valves452 a and 452 b. A first injector 466A is coupled in port 446 a, and asecond injector 466B is coupled in port 446 b. If desired, valve 424 maybe used to deactivate port 446 a under selected engine speed, load,and/or temperature conditions. Alternatively, a charge motion controlvalve may be used, if desired.

While FIG. 4 shows injector 466 a downstream of valve 424, it may alsobe placed upstream of valve 424 in an alternative embodiment.

In one embodiment, injector 466A injects a fuel having alcohol, such asethanol, methanol, or a mixture of gasoline with an alcohol (e.g., E85,M85, or other such blends and ratios), while injector 466B injectsgasoline. The gasoline injection may be performed at least partiallyduring conditions when valve 452 b is open. Alternatively, gasolineinjection from injector 466B may be performed at least partially duringconditions when valve 452 b is closed. In still another example,gasoline injection from injector 466B may be performed at leastpartially during conditions when valve 452 b is closed and at leastpartially during conditions when valve 452 b is open. In yet anotherexample, under some conditions open valve injection may be used while inother conditions closed valve injection may be used. Thus, the twoinjectors may be of a different type due to physical location, type ofsubstance being injected, operating strategy, etc.

In one example, the valve 424 may be adjusted to reduce airflow (i.e.,made more closed) under lower engine load conditions where fuel isprimarily provided by injector 466B. While a single valve is shown,multiple valves may be used if desired. Also, each cylinder may havesuch a valve, and each of such valves may be controlled by a singleactuation. In this way, it is possible to position a valve to obtain thedesired flow for the injectors that are active under differentconditions.

Referring now to FIG. 5, it shows a cylinder 530 with a single intakeport 546 of intake manifold 544 coupled respectively to intake valves552 a and 552 b. A first injector 566A and a second injector 566B arecoupled to port 546. If desired, valve 524 may be a charge motioncontrol valve which restricts flow around injector 566A to a greaterextent than injector 566B under selected engine speed, load, and/ortemperature conditions. Again, injector 566A injects a fuel havingalcohol, such as ethanol, methanol, or a mixture of gasoline with analcohol (e.g., E85, M85, or other such blends and ratios), whileinjector 566B injects gasoline. Thus, the two injectors may be of adifferent type due to physical location, type of substance beinginjected, mixture of substance being injected, heat of vaporization ofsubstance being injected, or operating strategy, etc.

FIG. 5 shows valve 524 being an elliptical valve with an asymmetricnotch 530 removed from the plate. The notch provides airflow nearinjector 566B whether the valve is open, closed, or partiallyopen/closed, yet can restrict airflow to a greater extent near injector566A. The valve rotates about an axis 532 in response to actuation bycontroller 12.

By adjusting valve 424 (or 524), it is possible to take advantage of thefact that at high loads, both ethanol injection and open (or partiallyopen) valve operation provide improved performance. At lower loads, thevalve(s) may be closed (or partially closed), and the gasoline injectorcan spray fuel into the active intake port, and the ethanol injector maybe deactivated. At higher loads, the valve would be open or partiallyopen, and ethanol could be injected into one port while gasoline isinjected into the other port.

Further, by using different operation of the two port injectors (e.g.,different timing, different fuels, different injectors for a cylinder,etc.) it is possible to reduce a compromise between package-space andair/fuel mixing. Further, it allows one injector to be placed in eachintake port, and ensures that fuel can always be supplied to a port thatis flowing air. By reducing airflow in a port when the injector is notinjecting fuel, it is possible to maintain acceptable air-fuel mixing inthe other port that is flowing air with injected fuel. Further, such anapproach may provide improved packaging compared with twin-sprayinjectors that may require a more central injector location between theports, making it more difficult to package two injectors per cylinder.

Referring now to FIG. 6, two fuel injectors are shown (610 and 612) withat least one different characteristic. Injector 610 may be used asinjector 66A, 466A, 566A, etc., while injector 612 may be used asinjector 66B, 466B, 566B, or vice versa, or combinations thereof, etc.The differing characteristic(s) between the injectors may be one or moreof the following: injector size, injector dynamic range, materials,minimum pulse width, injector slope (flow to pulse width), orifice size,spray pattern, spray pattern area, spray targeting, or others asdiscussed herein.

In one example, both injectors are sized to meet peak torquerequirements (for example a maximum airflow or aircharge). However, inan example where one injector provides gasoline and the other injectorprovides an alcohol blend (e.g., ethanol, E85, methanol, etc.), thepower densities of the fuels may be different. In such a case, theinjector for the alcohol based fuel may be sized to provide a differentmaximum fuel flow (e.g., approximately 37% higher to account for pureethanol).

Referring now specifically to FIG. 6, injector 610, which may be adirect cylinder injector or a port injector, is shown receiving acommand signal 620 from controller 12. Pressurized fuel is supplied toinlet 622, the flow of which is governed by an electromagnetic actuatorhaving coil 624, coupled to needle 626 cooperating with pintle 628. Theshape of pintle 628 may affect the spray geometry as well as the flowrate of the injector. Further, the size and shape of the needle may alsoaffect flow and spray patterns, as well as response time.

FIG. 6 also shows injector 612, with similarly labeled components,including a command signal 630, inlet 632, coil 634, needle 636, andpintle 638. As noted above, the pintles 628 and 638 may different insize, shape, material, or combinations thereof. Further, inlets 622/632,coils 624/634, and/or needles 626/636 may have different geometry,shapes, sizes, materials, weights, surface finishes, etc.

In this way, the respective injectors may be designed to providedifferent functionality and/or injection type (e.g., fuel type)compatibility so that improved engine operation and control may beachieved. As noted herein, an injection type may refer to differentinjection locations, different substances being injected (e.g., watervs. fuel), different fuel types being injected, different fuel blendsbeing injected, different alcohol contents being injected (e.g., 0% vs.85%), etc. Further note that different injection types may also refer todifferent substances being injected via a common injector, where a type1 injection may be a gasoline amount in the injection and type 2injection may be an alcohol amount in the injection.

Referring now to FIGS. 7-10, various fuel and vapor handling systems aredescribed. Specifically, FIG. 7 shows an example fuel pumpconfiguration, while FIGS. 8-10 show various fuel vapor purge systemconfigurations.

Referring now specifically to FIG. 7, an example fuel pump configurationis shown where a separate fuel pump and tank is provided for a first andsecond fuel type. Specifically, a first tank 710 is shown for holdingliquid fuel of a first type, with pump 712 leading to injector 66A viafuel rail 714. Likewise, a second tank 720 is shown for holding liquidfuel of a second type, with pump 722 leading to injector 66B via fuelrail 724. While the pumps are shown outside the tank, in an alternativeexample one or both of the pumps may be located within the tank.Further, a second, high pressure fuel pump may be added to one or boththe fuel lines downstream of respective low pressure pumps.

One or both the fuel systems may be returnless-type fuel systems,return-type fuel systems, or combinations thereof. Further, the fuelsystems may have different characteristics, such as different sizetanks, different size pump, different pump capacity, different pumppressure, different pump maximum flows, different on/off cycles (e.g.,pump 712 may run more intermittently than pump 722), etc. Note that insome examples, only one pump may operate under some conditions. Forexample, if fuel from tank 710 is not needed, or not enabled (e.g.,during cold start conditions), pump 712 may be deactivated (or notactivated) while pump 722 operates. In this way, less battery power maybe used, and less vapors may be generated.

In one example, the first tank contains an alcohol blend, such asethanol or an ethanol-gasoline mixture, while the second tank containsgasoline. However, other fuel types may also be used.

Referring now specifically to FIGS. 8-10, example fuel purging systemconfigurations are described in cases where two different fuel sourcesare provided, which may be in engines having two injectors per cylinder(e.g., a port injector and a direct injector, or two port injectors). Asnoted above, one fuel may be gasoline, where a second fuel may be analcohol or an alcohol blend. In such a case, the fuels may havedifferent volatility, vaporization, etc., which may be used toadvantage.

One example embodiment is shown in FIG. 8, in which a first tank 810 maybe used for a first fuel (e.g., gasoline) and tank 812 may be used for asecond fuel (e.g., ethanol). The tanks may be separate (as shown) orintegrally formed. Further, the size or volume of the tanks may bedifferent, for example tank 812 may be substantially smaller than tank810. In FIG. 8, tank 810 has a vapor conduit 820, tank 812 has a vaporconduit 822, both leading to junction 830. Junction 830 leads tocanister 814 (which can have a check valve venting to the atmosphere).Junction 830 may have a parallel conduit 826 leading to vapor managementvalve 816, which controls vapor flow to engine 10 (via intake manifold44, for example). In this way it is possible to enable vapor from bothtanks (or tank sections) to the engine using a single canister and asingle vapor control valve (although more canisters and/or valves may beused if desired).

However, one fuel may be more volatile than another fuel (for example,10% vaporization occurs at approximately 100 degF for gasoline vs 160degF for 85% ethanol). Thus, in this example, when tank 812 fuel levelis low, the total vapor volume (ullage space) of the system may berelatively high, which can make vapor control more difficult. Also, fuelfrom one tank may mix with a different fuel in the other tank (e.g.,contaminating the ethanol tank with excessive amounts of gasoline due toevaporation from the gasoline tank and condensation in the ethanoltank). Some of the above issues may be reduced by making the sizes ofconduits 820 and 822 relatively differently sized, for example.

Another approach that may be used is shown in FIG. 9. In this example,first tank 910 may be used for a first fuel (e.g., gasoline) and tank912 may be used for a second fuel (e.g., ethanol). The tanks may beseparate (as shown) or integrally formed. Further, the size or volume ofthe tanks may be different, for example tank 912 may be substantiallysmaller than tank 910. In the example of FIG. 9, separate canistersystems (e.g., canisters 914 and 916) may be used for each of tanks 910and 912. Specifically, tank 910 has a vapor conduit 920 leading tojunction 930, which is coupled to conduit 928 leading to canister 914(which then vents to atmosphere via a check valve). Further, tank 912has a conduit 922 which leads to junction 932, which then may lead tocanister 916 via conduit 924. Junction 930 also leads to a first valve940 via conduit 934, while junction 932 may lead to a second valve 942via conduit 926. Each of valves 940 and 942 are coupled to junction 946,which then leads to intake manifold 44 of the engine 10. Alternatively,each of valves 940 and 942 may be directed separately to separatelocations of the intake manifold. As above, additional canisters may beused, if desired. Further, canisters 914 and 916 may have differentcharacteristics (e.g., size, charcoal loading, storage capacity, orothers), and valves 940 and 942 may have different characteristics, suchas sizes, mounting orientations, maximum flows, minimum flows, orificeareas, actuation mechanisms, etc. Valves 940 and 942 may be completelyseparate, or may be packaged together in a single housing.

In this way, it is possible to enable vapor from both tanks (or tanksections) to the engine in controllable differential amounts whilereducing contamination from one tank to another tank.

FIG. 10 shows still another alternative embodiment, which is similar tothat of FIG. 9, yet a single vapor control valve is used, whilemaintaining separation between the two tanks (or tank sections).Specifically, in FIG. 10, tanks 1010 and 1012 are shown (which as notedabove may have different characteristics and may be separately orintegrally formed) along with canisters 1014 and 1016 (which also mayhave different characteristics). Tank 1010 is coupled to junction 1020via conduit 1022 and canister 1014 is coupled to junction 1020 viaconduit 1024 at a first outlet of the canister. A second outlet of thecanister 1014 is coupled to junction 1026, along with tank 1012 viaconduit 1028 and canister 1016 via conduit 1030. Further, junction 1020leads to valve 1040, which then directs flow to the engine intakemanifold.

In one example, a one-way check valve may be placed in line 1028 toreduce vapor flow from tank 1010 to tank 1012. Further, such a valve mayalso be placed in line 1022. However, the presence of canister 1014 maybe sufficient to reduce flow of vapors from tank 1010 to tank 1012, andvice versa.

In this way, a single valve may be used (although more may be added ifdesired), yet the system provides at least some separation between thetanks via a canister (in this example, canister 1014). Canister 1014 maybe sized large enough to reduce the amount of a first fuel vapor (e.g.,gasoline) that enters the tank 1012 to an acceptable level, and since itis in series with canister 1016, this can enable canister 1014 to have areduced size or capacity.

In any of the examples herein with more than one canister, the canistersmay be packaged in a single housing if desired.

As will be described in more detail below, control of fuel vapors,adaptive learning, vapor concentration learning, vapor blend learning,along with air-fuel ratio, may be affected by the fuel system type andconfiguration. For example, in some examples vapors from one or morefuel source may be concurrently delivered to the engine, in varyingamounts, and thus the controller may estimate the blend of the vapors(e.g., the percentage of alcohol in a gas/alcohol blend, for example) todetermine stoichiometry of the vapors, etc., that can then be used toadjust fuel injection, etc.

For example, under some conditions, purging of a first fuel type may beadvantageous, and under other conditions, purging of a second fuel typemay be advantageous. Further still, under still other conditions, bothtypes may be concurrently purged. Factors that may influence which ofthese are selected may include, for example, the amount of fuel vaporsof each being inducted. Thus, if the vapors contain mostly a fuelcorresponding to a first injector, purging from that source may be givenpreference and continued for a longer period, or performed with agreater purge flow rate, for example. Alternatively, an estimated blendin the reservoirs(s) may influence which reservoir is purged (and howmuch volume from that source is purged). For example, some reservoirsmay generate more vapors than other reservoirs, and thus need longer ormore frequent, or higher volume, purging.

Further, note that the desired/delivered amounts of type 1 and type 2injection, or for example, the relative amount of type 1 to type 2injection, may vary depending on the source of fuel vapors beinginducted into the engine. Thus, the injection amounts may be variedbased on the source of vapors, or based on whether any vapors are beinginducted into the engine, or based on the concentration of vapors beinginducted into the engine, and/or based on the blend of vapors beinginducted into the engine.

Referring now to FIG. 11, a routine is described for implementingadjustments in fuel injection amounts in response to feedback from anexhaust gas oxygen sensor (or other sources) to provide a desiredoverall air-fuel ratio. In particular, in cases where more than oneinjection type may be provided to a cylinder, the routine determineswhich type of fuel may be adjusted based on feedback. As used herein,different fuel or injection types may refer to different fuels (e.g.,alcohol containing fuels vs. gasoline) or may refer to differentinjector locations (e.g., port vs. direct), or may be different sizedinjectors (e.g., one having higher maximum flow than the other), or mayrefer to other injection characteristics, fuel delivery characteristics,spray characteristics, fuel property characteristics (e.g., temperature,heat capacity, power density, etc.) or may refer to gasoline injectionversus water injection, or others, or may refer to different fuel blends(where one fuel type has relatively more or less ethanol than anotherfuel type). Also, the fuel types may be separately delivered to thecombustion chamber, or mixed before delivery to the combustion chamber.

Specifically, in 1110, the routine determines whether injection ordelivery of fuel type 2 is enabled. As described in more detail herein,various factors may be used to determine whether to enable delivery orinjection of fuel type 2, such as engine temperature, exhausttemperature, an amount of type 2 injection (e.g., fuel type) on-board(e.g., in a fuel tank), etc. If the answer to 1110 is yes, the routinecontinues to 1112 to determine if injection or delivery of fuel type 1is enabled. Again, as described in more detail herein, various factorsmay be used to determine whether to enable delivery or injection of fueltype 1, such as engine temperature, exhaust temperature, an amount oftype 1 injection (e.g., fuel type) on-board (e.g., in a fuel tank), etc.If the answer to 1112 is yes, the routine continues to 1114, otherwisethe routine continues to 1116.

When the answer to 1110 is no, the routine continues to 1118 where againthe routine determines if injection or delivery of fuel type 1 isenabled. If not, the routine ends. Otherwise, the routine continues to1120.

In 1114, the routine selects a fuel type for adjustment as describedbelow in more detail with regard to FIG. 12. For example, if type 1 isselected, the routine continues to 1120, if type 2 is selected, theroutine continues to 1116, and if both fuel types are selected, theroutine continues to 1122. While the routine of FIG. 12 considersfactors such as a bandwidth of needed adjustments, minimum and maximumpulse width limits, and others, various other factors can influencewhich injectors are adjusted in response to feedback information, and/orrelative amounts of adjustment between multiple injectors based onfeedback information. In one embodiment where water is included in thetype 2 injection (e.g., a water-alcohol or water-ethanol mix),adjustment of type 2 injection in response to air-fuel ratio errorsbecomes decreasingly effective as the water fraction in the mixincreases. Thus, in such an embodiment, selection of type 2 injectionadjustment to affect air-fuel ratio (e.g., in response to exhaust gasoxygen sensor feedback) may be stopped or disabled when the waterfraction surpasses a limit, such as 0.7, for example, and thus all ormost all of the adjustments can be made with a type 1 injection, such asgasoline injection. Another criteria that may be used in selectinginjectors for feedback control may be based on how much fuel is in therespective tanks, and thus if one fuel is low, it may be not beincreased in response to feedback to conserve that fuel.

In 1116, the routine adjusts fuel type 2 based on air-fuel ratio sensorfeedback (see also FIG. 17). For example, a PI controller may be used toprocess an error signal (between a desired and measured air-fuel ratio)to generate a feedback correction to adjust an amount of injected ordelivered fuel of fuel type 2. Note also that more than one sensor maybe used to generate upstream and downstream feedback corrections.

In 1120, the routine adjusts fuel type 1 based on air-fuel ratio sensorfeedback (see also FIG. 17). For example, a PI controller may be used toprocess an error signal (between a desired and measured air-fuel ratio)to generate a feedback correction to adjust an amount of injected ordelivered fuel of fuel type 1. Again note that more than one sensor maybe used to generate upstream and downstream feedback corrections.

In 1122, the routine adjusts both fuel type 1 and 2 based on air-fuelratio sensor feedback (see also FIG. 17). For example, a PI controllermay be used to process an error signal (between a desired and measuredair-fuel ratio) to generate a feedback correction. The correction maythen be divided into two parts, one to adjust an amount of injected ordelivered fuel of fuel type 1, and another to adjust an amount ofinjected or delivered fuel of fuel type 2. Again note that more than onesensor may be used to generate upstream and downstream feedbackcorrections. Further, the upstream correction may be applied to fueltype 2 while the downstream correction may be applied to fuel type 1, orvice versa. In another example, lean corrections may be applied to fueltype 2 while rich corrections may be applied to fuel type 1, or viceversa to adjust a relative amount of fuel types. Also, greatercorrections may be made with fuel type 1 under a first set of selectedengine operating conditions, and greater corrections may be made withfuel type 2 under a second set of selected engine operating conditions.

In this way, different fuel types (e.g., injection locations, fuelqualities, fuel densities, fuel heat capacities, etc.) may be used underdifferent conditions and in different amounts to facilitate air-fuelfeedback corrections depending on operating conditions.

Referring now to FIG. 12, an example routine for selecting which fueltype to use for feedback adjustment of air-fuel ratio is described. Asnoted above, various factors may be considered, and while the routinedescribed in FIG. 12 shows some of these factors, others may also beadded, or only some or none of the factors shown may be considered, ifdesired.

In 1210, the routine reads exhaust air-fuel ratio sensor informationfrom one or more exhaust gas sensors. Then in 1212, the routinecalculates an amount and direction of correction or corrections. Forexample, a PI controller may be used, or multiple PI control loops maybe used, such as based on upstream and downstream sensors. Then, in1214, the routine determines whether a high frequency adjustment isrequired in the amount of fuel delivered. For example, if a rapid (andpossibly large) change in exhaust air-fuel ratio is encountered, it maybe possible to more rapidly correct this error using type 2 injection(e.g., fuel type, such as when type 2 fuel is injected directly, orinjected more closely to the cylinder, or if an injector for type 2 fuelhas a higher bandwidth than an injector for type 1 fuel). If the answerto 1214 is yes, the routine continues to 1216 to select type 2 fueladjustment and then ends.

Otherwise, the routine continues to 1218 to determine if a correspondingpulse width (PW) of the injector for the type 1 injection is near aminimum PW value for the injector or a maximum PW for the injector. Ifso, the routine again proceeds to 1216. If the answer to 1218 is no, theroutine continues to 1220 to determine if a corresponding pulse width(PW) of the injector for the type 2 injection is near a minimum PW valuefor the injector or a maximum PW for the injector. If so, the routineproceeds to 1222 to select type 1 fuel for adjustment. If the answer to1220 is no, the routine continues to 1224.

In 1224, the routine determines whether conditions are present to adjustboth fuel types based on feedback information. For example, it may bedetermined that higher frequency adjustments be made with type 2injection (e.g., fuel type) adjustments and lower frequency adjustmentsbe made with type 1 fuel adjustments. In this way, in the example wheretype 2 injection is direct fuel injection and type 1 injection is portfuel injection, wall wetting dynamic delays can be reduced.Alternatively, both fuels may be selected for adjustment, where aportion of the adjustment is made by each fuel type. This portion, whichmay be a percentage or other ratio, may be adjusted with engineoperating conditions, fuel conditions, etc.

If the answer to 1224 is yes, the routine continues to adjust both fuelsin 1226. Otherwise, the routine continues to 1228 to adjust fuel type 1.

In this way, different fuel types can be used to provide air-fuelfeedback control for different conditions so that overall operation isimproved. For example, where port injection is used to control lowerfrequency feedback adjustments than direct injection, faster feedbackcontrol can be achieved while reducing wall wetting dynamics, and stillutilizing feedback adjustment of both fuel types. Further, issues withminimum or maximum injector fueling can be addressed, while stillmaintaining accurate overall air-fuel ratio control.

Referring now to FIG. 13, a first embodiment example starting routine isprovided for enabling fuel types based on engine, vehicle, and/orambient operating conditions. First, in 1310 the routine determineswhether an engine start has occurred. For example, the routine canmonitor engine speed, cranking motor, key-on operation, or various otherparameters to identify an engine start. If the answer to 1310 is yes,the routine continues to 1312 to enable fuel type 1 delivery orinjection. Then, the routine continues to 1314 to determine whetherengine coolant temperature (ECT) is greater than a limit T1. If so, theroutine continues to 1316 to determine whether catalyst temperature isgreater than a limit T2. If so, the routine continues to 1318 to enablefuel type 2 delivery or injection. In this way, it is possible toutilize fuel type 1 for engine starting and/or engine warm-up, and avoidfuel type 2 until the engine and exhaust system have warmed, for caseswhere fuel type 2 is more difficult to vaporize, such as an alcoholcontaining fuel (e.g., ethanol or an ethanol blend), for example. Asnoted above, the fuel types may refer to different fuel blends,different injector locations, etc.

While the above example relies on engine coolant temperature, variousother parameters may be used, such as ambient air temperature, ambientpressure, oil temperature, etc. Likewise, various exhaust temperaturesmay be used, such as exhaust gas temperature, catalyst temperature, orestimates thereof. In this way, it is possible to provide an appropriatefuel for engine starting and/or warm-up. Further, the startingapproaches herein may be used for re-starting, such as a hot-restart, are-start after an unsuccessful start, starting after deceleration fuelshut-off, or starting an engine during rotation or from rest, such aswith a hybrid vehicle (e.g., hybrid-electric vehicle).

Referring now to FIGS. 14-15, a second embodiment for enabling fueltypes is described that accounts for limiting some fuel types duringengine warm-up/starting operation. In this embodiment, a warm-upstrategy is described which can apply to various engine concepts usingat least two fuel types, such as two PFI injectors per cylinder, one DIand one PFI injector per cylinder, or one ethanol blend injector and onegasoline injector, etc. In this way, engine control strategy can beincluded to prevent use of a fuel type (such as an ethanol blend) whenthe engine is too cold, and transition (gradually or abruptly) towardsusage as the engine warms up. This can be done for at least thefollowing reasons. (1) In the example where ethanol or an ethanol blendis used, such fuel can be less volatile than gasoline (e.g., 10%vaporization occurs at approximately 100 degrees F. for gasoline vs. 160degrees F. for 85% ethanol). Attaining adequate vaporization andair-fuel mixing with ethanol may be difficult before the engine iswarmed up. (2) Again, in the example where ethanol is used to avoid orreduce knock under selected conditions, the likelihood of knock is maybe greatly reduced at cooler temperatures. Thus, it may be desirable,under some conditions, to minimize ethanol consumption when possible, toconserve it for times when knock is more likely.

As will be described in more detail below, once the engine is warmed up,a desired ethanol fraction (EF), or other such parameter, can bedetermined as a function of speed and load as described, with additionallogic for unusual ambient conditions, low fuel level of ethanol orgasoline, etc. The warmed-up desired ethanol fraction can then bemodified with one ore more multipliers (e.g., an overall multiplierEF_MUL) to account for cold start and warm-up.

The value of EF_MUL can be in the range between zero and one duringwarm-up (values higher than one may be desired for higher-than-normaltemperatures). The value of EF_MUL can be determined from a variety ofinputs, including engine coolant temperature, engine oil temperature,ambient air temperature, engine intake air temperature, time sinceengine start, speed, load, available fuel pressure, ambient humidity,and other parameters. Each of these inputs could be measured orinferred. The value of EF_MUL can be continuously re-calculated duringengine operation.

Referring now specifically to FIG. 14, in 1410 the routine determineswhether an engine start is present. Then, if so, in 1412 a time sinceengine start timer is reset to zero and starts counting. Likewise, acombustion event counter is reset to zero and starts counting combustionevents from the start.

From either 1412 or when the answer to 1410 is no, the routine continuesto 1414, 1416, and 1418 to calculate individual multipliers for the type2 injection using the calibration graphs of FIG. 15, which in oneexample is an ethanol or ethanol blend, or another alcohol containingblend. The routine then continues to step 1420.

In one embodiment of step 1420, the routine determines a current valueof the overall multiplier on a desired fuel type 2 fraction bymultiplying the values of the separate multipliers for each input. Inthis method, the effects of the input variables can all be accounted forsimultaneously, for example:EF _(—) MUL=EF _(—) MUL _(—) ECT*EF _(—) MUL _(—) EOT*EF _(—) MUL _(—)AAT*EF _(—) MUL _(—) ACT*EF _(—) MUL _(—) ATMR1

Where

EF_MUL=Overall multiplier on desired ethanol fraction,EF_MUL_ECT=Multiplier as a function of engine coolant temperature,EF_MUL_EOT=Multiplier as a function of engine oil temperature,EF_MUL_AAT=Multiplier as a function of ambient air temperature,EF_MUL_ACT=Multiplier as a function of engine intake air temperature,EF_MUL_ATMR1=Multiplier as a function of time since engine start ornumber of combustion events since engine start.

Example calibrations for these multipliers are illustrated in the top,middle, and bottom graphs of FIG. 15. The graphs show linear changes foreach input, but the actual calibration may be non-linear. The valuescould be determined from look-up tables, from mathematical equations,etc. Note that the minimum calibration of EF_MUL_ATMR1 could beconstrained by the time required to build up sufficient ethanol fuelpressure to operate the direct injection system, or an additionalmultiplier could be used for fuel pressure. Also, some or all of themultipliers may be calculated using more than one input. For example,fuel/air mixing at low temperatures may only be an issue in certainranges of speed and/or load. Also, while each graph is the same for twomultipliers, each multiplier may have a different calibration inpractice.

Note that the above multipliers may also be a function of additionalparameters, such as a number of combustion events from an engine start.

An alternative embodiment of step 1420 is described for limiting a fueltype during engine warm-up. Specifically, in this embodiment, each inputfactor is considered as a separate possible constraint on a fuel typeuse (e.g., ethanol use). The current value of the overall multiplier(for the desired ethanol fraction) can be determined by the input factorwhich is currently the most constraining. This may involve examining thesame input multipliers as above, although the calibration values ofthese multipliers may be chosen differently. Also, the value of EF_MULmay be continuously re-calculated during engine operation. For example,the following calculation may be used:EF _(—) MUL=MINIMUM(EF _(—) MUL _(—) ECT,EF _(—) MUL _(—) EOT, EF _(—)MUL _(—) AAT, EF _(—) MUL _(—) ACT,EF _(—) MUL _(—) ATMR1)

With this method, when the engine is first started, EF_MUL_ATMR1 may bethe limiting constraint, followed by EF_MUL_ECT until the coolant warmsup, followed by EF_MUL_EOT until the oil warms up, and then theremaining constraint may by EF_MUL_AAT in very cold weather.

Referring now to FIGS. 16-18, a routine is described for selecting aninitial desired relative amount of fuels, and then taking into accountone or more multipliers such as those discussed above, as well as otherconditions. Further, the routine then performs several adjustments, ifnecessary, to account for fuel storage quantities and other factors, andthen uses the values to coordinate engine operation to meet driverrequests.

In 1610 the routine reads various engine operating parameters, such asengine speed, engine load, engine coolant temperature, exhausttemperature, gear ratios, etc. Then, in 1612, the routine selects aninitial type 1 and type 2 relative amounts, such as a desired fractionbased on the operating parameters. Note that various alternativedeterminations may be made, such as determining a desired percentage offuel types, or absolute amounts of fuel types. Further, an adaptiveparameter may also be included to account for learned adjustments to thefuel types based on feedback from various sensors, such as a knocksensor. The adaptive terms may be stored as a function of speed, load,temperature, or combinations thereof, for example. In this way, if knockconsistently occurs in repeatable locations, an automatic increase inthe amount of type 2 injection, for example, may be adaptively learnedso that such adjustment can be made without waiting for feedback from aknock sensor.

In one example where type 2 injection is ethanol (or an ethanol blend),the determination in 1612 may be referred to as a desired ethanolfraction (EF). Note, however, that it may be a weight percent, masspercent, volume percent, or ratio. Further, absolute values may also beused, if desired, as noted herein. Further, the selection of the amountsof type 1 and type 2 injections may be based on other factors, such asfactors that can affect a tendency for knock. For example, ambienthumidity may be used to adjust an amount of type 2 injection for givenoperating conditions, as increased humidity can decrease knock tendency(and thus less type 2 injection may be needed), and vice versa. Notethat a desired spark timing may also be varied as the relative amountsof type 1 and type 2 injection are varied, or as the individual amountsof the type 1 and type 2 injections are varied.

In one example, the amount of type 2 fuel may be determined based oncompression ratio, boosting, and temperature so that engine knock may bereduced thus reducing a limit of spark advance. However, as notedherein, additional factors may be used in determining whether to usetype 2 fuel, and the amount of type 2 fuel, such as, for example, theamount of type 1 fuel remaining in the tank, the need to learn thecontent (e.g., blend) of type 2 fuel on-board, minimum pulsewidthissues, and a need to periodically operate with type 2 fuel if it hasnot been used frequently enough (e.g., to reduce deposit formation andor clogging of fuel lines and/or injectors).

In another example, which may be used in addition to the examples andembodiments noted herein, transient conditions may be detected and usedto initiate an open-loop adjustment in the amount of type 2 (and type 1)injection. The adjustment may be include a temporary increase in arelative amount of type 2 injection in response to the transientcondition detection. In one embodiment, a driver tip-in, such as a rapidtip-in from idle conditions, may be detected. In response to suchconditions, a type 2 injection (e.g. direct or port injection of analcohol-containing mixture, e.g., ethanol or an ethanol blend) may betemporarily increased with a predetermined or actively varying profile.In this way, the heat capacity/heat of vaporization of substances, suchas fuel, injected into the engine may be increased, thereby reducing atendency for tip-in knock. As one example, EF may be temporarilyincreased by 5-10 percent for one to 10 combustion cycles in response toa driver tip-in.

Continuing with FIG. 16, in 1614, the routine adjusts the initial amountbased on various factors, such as the multipliers discussed above withregard to FIGS. 14-15. For example, the minimum multiplier may be used,or all multipliers together may be used, as discussed above. Next, in1616, the routine continues to determine whether type 2 fuel is empty(e.g., the storage location is empty or below a minimum value) ordisabled. If so, the routine continues to 1618 to set the adjustedinitial relative amount (e.g., EF) to zero. Alternatively, the routinecontinues to determine in 1620 whether type 1 fuel is empty (e.g., thestorage location is empty or below a minimum value) or disabled. If so,the routine continues to 1622 to set the adjusted initial relativeamount (e.g., EF) to 1 (or 100%). Finally, the routine continues to 1624to output the adjusted relative amount of fuel types. In this way, it ispossible to account for various operating factors and/or situations indetermining amount of fuel types to be used during engine operation.

The routine then continues to 1710 in FIG. 17 to determine a desiredengine torque. The desired engine torque may be based on a driverrequest, engine speed, gear ratio, cruise control, traction control,vehicle stability control, etc. Then, in 1714, the routine determines adesired air-fuel ratio based on operating conditions. For example, lean,rich, or near stoichiometric conditions may by selected. Then, in 1716,the routine reads the relative amounts type 1 and type 2 fuels from1624, which accounts for warm-up effects and fuel availability.

In 1718, the routine determines feedforward amounts of type 1 and type 2injections based on the relative amount, desired torque, desiredair-fuel ratio, and/or other operating conditions. For example, theroutine can determine a total amount of fuel energy that needs to beprovided to provide the desired engine torque, and then proportion thefuel energy among the fuel types based on the desired ratio (or relativeamount) of the fuel types taking into account different power density,fuel density, etc. of the fuel types, if present. Further, the routinecan then determine an initial fuel amount for each fuel type, that whensupplied to the engine at the current conditions, produces the desiredtorque, assuming sufficient air is present. The fuel amounts may be invarious units, including a corresponding fuel pulse width (PW) given theinjector characteristics for the fuel type, thus taking into account aninjector slope and offset, for example.

Next, in 1720, the routine adds feedback air-fuel ratio adjustments toone or both of the fuel amounts. As described herein, the feedbackadjustments may be based on air-fuel ratio sensors in the exhaust, andadjustments may change between different fuel types under differentconditions. Again, the adjustments may be in various units, includingpulse width (PW).

Continuing with FIG. 17, in 1722 the routine determines whether the type2 pulse width is less than a minimum value (min_pw_2 for the type 2injector). If so, the routine continues to 1724 to increase the type 2fuel amount (e.g., PW) and decrease the type 1 fuel amount by acorresponding amount. In this way, in the example where type 2 fuel isused to decrease a tendency of knock, the system errs on providingadditional type 2 fuel so that knock is reduced and operating at lowpulse width values is also reduced or avoided.

Alternatively, if the answer to 1722 is no, the routine continues to1726 to determine whether the type 1 pulse width is less than a minimumvalue (min_pw_(—)1) for the type 1 injector. If so, the routinecontinues to 1728 to decrease the type 1 fuel amount (e.g., PW) to zeroand increase the type 2 fuel amount by a corresponding amount. Again, inthis way, in the example where type 2 fuel is used to decrease atendency of knock, the system errs on providing additional type 2 fuelso that knock is reduced and operating at low pulse width values is alsoreduced or avoided.

From either 1728 or when the answer to 1726 is no, the routine continuesto 1730 to determine an air amount based on the desired air-fuel ratioand the stoichiometric air-fuel ratio of the actual mixture provided viatype 1 and type 2 injectors. The airflow can then be provided via anelectronically controlled throttle, valve timing, or other suchactuator.

In this way, it is possible to account for varying relative amounts offuel types and varying total fuel amounts, while compensating forminimum fuel limits and providing a desired engine torque at a desiredair-fuel ratio.

Referring now to FIG. 18, a routine is described for compensating forlimits on the ability to use different fuel types under differentconditions and compensate for the potential of engine knock. Forexample, in the case where a type 2 injection is used to reducelikelihood of knock (e.g., directly injected ethanol or an ethanolblend), limiting the used of such a fuel under selected conditions,along with other conditions (e.g., increased compression ratio,boosting, etc.) may result in knock occurring. In other words, in theexample where ethanol is limited until the engine is warmed up, thecontrol strategy may account for the effect of reduced ethanol on engineoperation. And, if one purpose of ethanol is to enable increasedcompression ratio and/or increased boost pressure (because of ethanol'shigher octane and higher heat of vaporization), when ethanol use isbeing limited (EF_MUL<1), it may be necessary to take additional controlactions to avoid or reduce knock (despite the decreased knock tendencyat lower temperatures). In one embodiment, feedback knock control wherespark timing is adjusted in response to a knock sensor may be used.Alternatively, or in addition, open-loop knock avoidance may also bedesired to provide a starting point for the closed-loop knock controlsystem and/or as a back-up system for times that the closed-loop knockcontrol system is degraded.

One approach to open-loop knock avoidance when EF_MUL is less than onecan be provided with a combination of additional spark retard,additional enrichment, transmission downshifting (to increase enginespeed, because knock may be less likely at higher speeds), load limitingwith electronic throttle, and/or boost limiting via wastegate orvariable geometry turbocharger adjustments. Depending on operatingconditions (e.g. compression ratio and/or boost pressure), variouscontrol strategies could be used.

In a first embodiment, sensitivity of knock-limited spark advance may bemapped to a number of variables, such as RPM, torque, air/fuel ratio,engine intake air temperature, and also the amount of ethanol reduction(e.g., EF_MUL) or ethanol fraction as an additional variable.

In a second embodiment, where spark retard alone to avoid knock may beinsufficient (e.g., excessive spark retard can cause surge and/or highexhaust temperature), additional modifications may be made. For example,the routine can first retard spark as much as feasible, then enrich thecombustion air-fuel ratio to avoid or reduce knock. If the maximumfeasible enrichment is encountered, then a transmission downshift may becommanded.

In a third embodiment, the routine can first retard spark as much asfeasible, then command a transmission downshift. If there is still apotential for knock, the routine can then enrich enough to avoid orreduce knock.

In a fourth embodiment, the routine can limit maximum load withelectronic throttle control. Such an approach may be used alone, or incombination with one of the first, second, and/or third embodiment aboveif those approaches provide insufficient knock control (because limitingmaximum load may cause degraded driver satisfaction). The maximumallowed load can be mapped as a function of EF_MUL or ethanol fraction,engine speed, engine coolant temperature, relative air/fuel ratio, andother variables. For example, the following function may be used:MAX_LOAD=f(EF _(—) MUL or EF,RPM,ECT,a/f, etc.)

In a fifth embodiment, the routine can limit maximum boost with thewastegate and/or compressor bypass valve. Again, such action may be usedalone, or in addition to one of the four embodiments above, if thosestrategies provide insufficient knock control (again because limitingmaximum boost may cause driver dissatisfaction). The maximum allowedboost can be mapped as a function of EF_MUL or ethanol fraction, enginespeed, engine coolant temperature, relative air/fuel ratio, and othervariables, as:MAX_BOOST=f(EF _(—) MUL or EF,RPM,ECT,a/f, etc.)

Numerous variations on these embodiments are possible, for example thesecond and third embodiments could omit either downshifting orenrichment.

Referring now specifically to FIG. 18, in 1810 the routine compares thefinal type 1 and type 2 injection amounts to the initial amounts fromFIG. 16. For example, the routine may determine a difference by whichthe fuel types have been adjusted, which may increase a tendency forknock based on the current operating conditions. Then, in 1812, theroutine determines whether this difference is too great for the currentconditions (e.g., the routine may make an open-loop estimate of whetherknock may be encountered). If so, the routine continues to 1814 toadjust an operating parameter to reduce the tendency for knock, such asthe five embodiments discussed immediately above herein.

In this way, even when the desired amount of type 2 injection to reduceknock is not available, knock may still be reduced in an efficientmanner.

Referring now to FIG. 19, a routine is described for dealing withdifferent levels of fuel or injection types during an engine start, andmore particularly if a fuel type becomes unavailable since the storageis empty. For example, previous engine operation may result in depletingone fuel type. However, due to the approach described herein, it may bepossible to run out of one fuel type without forcing an engine shutdown.Then, the routine of FIG. 19 may be used to decide when to allow theengine to run (or start) when one fuel tank is empty, or when one fueltype is depleted. The routine of FIG. 20 may be used to adjust currentengine operation if a fuel type is depleted during engine operation.

Returning to FIG. 19, the routine first determines whether an enginestart is requested (e.g., by monitoring key position, etc.). If so, theroutine continues to 1912 to determine if the driver is attempting tostart the engine when a first fuel type is depleted (e.g., a gasolinefuel tank is empty). If so, the routine continues to 1914 to determinewhether to start on a type 2 fuel (e.g., ethanol, an ethanol blend,another alcohol containing fuel or blend, a different injector location,etc. The decision of 1914 may be based on a probability of successfulstarting using the type 2 fuel, and/or a probability of achievingacceptable exhaust emissions. Both of these factors may depend onfactors such as temperature (of engine coolant and/or engine oil and/orengine intake air), and can be determined from:START_PROB=f(ECT,EOT,ACT)EMIS_OK_PROB=f(ECT,EOT,ACT)

If the probability of a successful start is below a threshold (i.e.,answer to 1914 is no), then the engine can be cranked without any fuelinjection (or operating only injectors for fuel type 1. If theprobability of a successful start exceeds the threshold, then a startcan be attempted With type 2 fuel in 1918. If a start is attempted butthe probability of acceptable exhaust emissions is low, then anindicator light may be activated alerting the driver and an error codecan be set.

In this way, it may be possible to provide an engine start even if afuel type is depleted, while avoiding attempting starts under conditionin which the remaining fuel type may cause degraded or unacceptableperformance.

In one embodiment, when the answer to 1914 is yes, the routine maycontinue to 1920 to determine whether starting on both type 1 and type 2fuel types may be performed. Such operation may desirable under selectedconditions, such as based on ECT, EOT, ACT, barometric pressure, orcombinations thereof. If so, the routine may proceed to 1922 to crankwith both fuel types. And if not, the routine proceeds to 1918 asindicated above.

Referring now to FIG. 20, a routine is described for adjusting operationif an injection type is depleted, such as in the case where a firstreservoir coupled to a first injector contains gasoline or a gasolineblend, and a second reservoir coupled to a second injector contains analcohol blend, such as an ethanol blend, or simply ethanol. Note,however, that the routine can apply to various other situations, such aswhere the second reservoir contains water or a water blend, for example.

First, in 2010 the routine determines respective reservoir levels of atleast a first and second reservoir. As noted herein, the reservoirs mayseparately hold different fuel blends, where one reservoir is largerthan another reservoir, which may be referred to as primary andsecondary reservoirs, respectively. Next, in 2012, the routinedetermines whether the primary reservoir is empty. For example, theroutine may determine the reservoir is empty if the fluid level is belowan empty threshold, or if an estimate of the amount of fluid usedreaches a preselected value, without a refilling event. If not, theroutine continues to 2014 to determine whether the secondary reservoiris empty. Again, this may be determined in various ways. If so, theroutine continues to 2024, otherwise the routine continues to 2016. Inone example, the values that would be considered “low” for eachreservoir level could be calibratable so that unmodified injection andengine function could be maintained for a majority of operation, orcould be set so that it is maintained as long as possible.

In 2016, the routine determines whether the primary reservoir is low.For example, the routine may determine the reservoir is empty if thefluid level is below a low threshold, or if an estimate of the amount offluid used reaches a second preselected value, without a refillingevent. If so, the routine continues to 2028. If not, the routinecontinues to 2018 to determine whether the secondary reservoir is low.Again, this may be determined in various ways. If so, the routinecontinues to 2020, otherwise the routine continues to 2022.

In 2020, the routine determines whether the manifold absolute pressurelevel, and/or boosting level, can be maintained without enrichment ifthe secondary injection is not used. In other words, the routinedetermines whether the secondary injection is needed to avoid knockwithout adjusting using enrichment and/or spark retard, for example. Ifthe answer to 2020 is yes, the routine continues to 2022. In 2022, theroutine continues to use the injection amounts determined herein withoutmodification. Otherwise, the routine continues to 2024 to disable thesecondary injectors to one or more cylinders and adjust the primaryinjection amount in 2026. Specifically, the primary injection isadjusted to compensate for the reduction in secondary injection in termsof air-fuel ratio, torque production, etc. Further, additionaladjustments may also be used, such as spark adjustments, throttle angle,boost pressure, or combinations thereof.

Continuing with FIG. 20, in 2028 and 2030, when the primary reservoir islow, the routine reduces primary injection and increases secondaryinjection. Specifically, the routine adjusts the secondary injection tocompensate for the reduction in primary injection on parameters such asair-fuel ratio, torque, etc. In this way, it is possible to reduce usageof the primary reservoir, without increasing a potential for knock. Notethat the amount of increase/reduction in 2028 may be based on variousfactors, such as engine speed and load, vehicle speed, etc. Further,additional adjustments may be used to compensate for theincrease/decrease, such as boost pressure, spark retard, throttle angle,etc. For example, as the secondary injection increases, allowable boost(without encountering knock) may be increased.

In general terms, the routine of FIG. 20 can operate to first depletethe secondary reservoir before depleting the primary reservoir, at leastin one embodiment. Such an approach can be desirable where the primaryreservoir contains a fuel that is the fuel used for starting (e.g., thesecond reservoir contains a fuel with less volatility). In this way, ifthe vehicle is shut-off without refueling, engine starting may still beprovided under a greater range of conditions.

Further, once it has been determined that the secondary supply isrunning low, the goal of the control system could be to maintainstoichiometric operation as long as possible to maintain emissionsperformance. The operating conditions could be evaluated to determine ifthe desired torque (or close to the desired torque) could be achievedwith spark retard and without (or with reduced) fuel enrichment. If thedesired torque could be obtained by increasing boost and retardingspark, then the secondary injection (e.g., ethanol or an ethanol blend)could be disabled. However, if enrichment is needed, then the secondaryinjection could be used. In such a circumstance, acceptable operatingconditions in which the secondary injection is disabled could be mappedto determine acceptable spark, fuel, throttle, and boost settingswithout the secondary injection (e.g., without ethanol or with reducedethanol). Then, once the secondary reservoir was depleted, the enginecould still operate, but with potentially reduced maximum engineperformance and/or reduced fuel economy (because of the potential needfor additional fuel enrichment and spark retard to counteract knock).

In this way, it is possible to take advantage of multiple reservoirswith different fuel blends to extend engine operation and performanceand/or efficiency gains over a greater range.

Referring now to FIG. 21, a graph illustrates different injectorcharacteristics for two example injectors via lines 2110 and 2112. Inone example, injector line 2110 can be for type 2 injection (e.g.,ethanol, direct injector, water injection, etc.), while line 2112 can befor a type 1 injection (e.g., gasoline, port injector, gasoline blend,etc.). While this example shows each injector having the same minimumpulse width (minpw1), in another embodiment they may have differentminimum pulse widths. The graph also illustrates how the injectors aresized for different maximum fuel flows, with different injector slopes.As noted herein, the air-fuel ratio feedback control gains and/oradaptive learning gains for the different injectors may be different toaccount for the variation in injector slope and/or offset (minimum flowvalue), as well as different fuel characteristics.

Referring now to FIG. 22, a graph is shown illustrating an exampledetermination of an amount of type 2 injection (e.g., ethanol, anethanol blend, direct injection, open valve port injection, etc.) inresponse to a determination of knock tendency (e.g., as torqueincreases, as speed reduces, as temperature increases, as humiditydecreases, and/or combinations thereof). The graph illustrates with line2210 (versus 2212) that when first phasing in ethanol (in addition togasoline) at medium to high load, for example, near zero ethanolinjection may not be feasible. As such, the control system adds aselected amount of ethanol at or near the minimum pulse width. In thisway, for example, it is possible to provide sufficient ethanol to reducetendency for knock without violating the minimum stable pulsewidth ofthe ethanol injectors.

Note that in the examples described in FIGS. 21 and 22, a single slopewas used in the fuel injector response diagram. However, the graph maybe non-linear, and for example may have two linear segments, each withits own slope and offset. Further, the graph may also have a curvedresponse.

Referring now to FIG. 23, an alternative embodiment is described forcontrolling fuel injection of a first and second injection type, takinginto account minimum pulse width issues and different fuel typecharacteristics. First, in 2310, the routine determines a desiredfraction of a fuel type, for example ethanol fraction (EF). Next in2312, a desired overall air-fuel ratio, or relative air-fuel ratio, isdetermined. Desired overall relative air-fuel ratio can be determined asa function of speed, load, inferred exhaust temperature, etc. Thedesired ethanol fraction can be determined primarily as a function ofspeed and load as described herein, with additional logic for start andwarm-up, variable ambient conditions, low fuel levels of ethanol orgasoline, etc.

Next, in 2314, the routine calculates an overall stoichiometric air/fuelratio for the EF of 2310 as:AF_stoich_total=(1−EF)*(AF_stoich_gas)+(EF)*(AF_stoich_(—) eth)

where AF_stoich_total is the overall stoichiometric air/fuel ratio,AF_stoich_gas is the stoichiometric air/fuel ratio for a first fuel type(e.g., for gasoline approx. 14.6), AF_stoich_eth=stoichiometric air/fuelratio for a second fuel type (e.g., 9.0 for pure ethanol, approx. 9.8for E85), and EF=desired ethanol fraction from 2310 (or in general,desired fraction of the second fuel type). Note that the stoichiometricvalues for gasoline and ethanol could be modified based on adaptivelearning with feedback from exhaust oxygen sensors.

Next, in 2316 the routine calculates a desired fuel mass flow for thegasoline injector (which may be a port injector) and for the ethanolinjector (which may be a direct injector) as:fuel_mass_total=air_mass/[(AF_stoich_total)*(lambda)]fuel_mass_gasoline=(1−EF)*(fuel_mass_total)fuel_mass_ethanol=(EF)*(fuel_mass_total)

where

lambda is a desired relative air-fuel ratio from 2312, AF_stoich_totalis an overall stoichiometric air/fuel ratio from step 2314, and air_massis an air mass entering the cylinder to be fueled, which may be measuredor inferred.

Continuing with FIG. 23, in 2318, the routine then calculates fuelinjection pulse width commands for the two injectors based on fuelmasses calculated in 2316. Further, the routine includes adjustments tomaintain the ethanol injection at least at the minimum pulse width (byreducing gasoline pulse width if necessary, or by turning off thegasoline injection if it reaches a minimum pulse width and increasingethanol pulse width accordingly, as noted above herein with regard toFIGS. 17 and 22, for example).

Referring now to FIG. 24 et seq., routines and graphs are shown for anexample where a first injection type is gasoline or diesel fuel, and asecond injection type includes water, such as pure water, a water andalcohol blend, or a water and ethanol blend, or a water and methanolblend, or others as noted herein. Further, in one embodiment, type 1injection is port injected fuel to a cylinder, while type 2 injection isdirectly injected fuel to the cylinder. In another embodiment, bothtypes of injection can be port injection, such as shown in FIG. 4 or 5.

As discussed herein, a possible benefit of multiple fuel types, such asusing gasoline and ethanol, is that knock may be suppressed underconditions where it may otherwise occur due to a combination of higherfuel octane and increased charge cooling (e.g., due to the ethanol'shigher heat of vaporization). The charge cooling effect may also beenhanced by providing the charge cooling effect mostly by the air, withlittle or no evaporation from metal surfaces like the intake manifold,via direct injection or targeted port injection with open valveinjection.

However, ethanol (or other alcohol based fuels) may be expensive orunavailable at some times and/or locations. Thus, if relying on suchfuels, if they are unavailable, engine torque and/or performance may belimited. To reduce or eliminate such torque and/or power limitations,one approach could include added hardware and/or control logic to allowuse of water (or water/ethanol, or water with an alcohol containingmixture, or other mixtures) in the second (e.g., ethanol) fuel system.

For example, water, or a water mixture, could attain part or all of theknock benefit of ethanol at high loads. Although water has no specificoctane value, it does have a higher heat of vaporization (approximately2256 kJ/kg, compared to approximately 840 for ethanol and approximately350 for gasoline). Therefore, by enabling injection (direct or port) ofwater (or a water alcohol mixture), similar knock improvements may beachieved. Further, an additional benefit of water/ethanol flexibilitymay be the ability to use very late injection of water (when the tank isfilled with mostly water). Late injection could be used for exhausttemperature control and/or increased boost at low RPM and/or reducedturbo lag.

In one approach, when enabling a second injection source to have avarying ratio of water and an alcohol blend (e.g., water and ethanol, orwater and an ethanol/gasoline blend), it may be beneficial to be able tomeasure or infer the Water Fraction (WF) in the ethanol/water fuel tank,or conversely, the ethanol fraction. WF may vary from zero (pureethanol) to one (pure water), in this example. This information can thenbe used for various features, including determining the desired amountof gasoline and the water/ethanol blend to provide a desired torquewhile reducing knock, and also to maintain accurate control ofcombustion overall air/fuel ratio.

In one embodiment, a sensor could measure one or more properties thatdiffer between water and ethanol, for example any of the following, orcombinations thereof, may be used: specific gravity (about 1 for water,and about 0.789 for ethanol), viscosity (about 21 lb-s/ft2 for water andabout 25 for ethanol), capacitance, resistance, or others. Sensorreadings may use compensation for temperature and other changes thataffect the properties of water and/or ethanol, if desired.

In another embodiment, an inferred estimate of the water fraction (WF),or equivalent parameter may be used. One process of inferring WF mayinclude performing the estimate at specific times, for example aftereach engine start and/or after a refueling event is detected via fuellevel sensor. The WF inference process can occur when the engine isrunning on gasoline in closed-loop air/fuel control (e.g.,stoichiometric feedback control), with vapor purge disabled.

The WF inference process may include gradually increasing pulse width onthe water/ethanol injector(s) while maintaining an overallstoichiometric air/fuel ratio based on closed-loop control using exhaustoxygen sensors via corresponding reduction of the gasoline injectionpulse width. The pulse width values and/or changes of the gasoline andwater/ethanol injectors can then be used to calculate WF. For example,if the pulse width of the water/ethanol injectors can be greatlyincreased and/or decreased with no or minimum decrease and/or increasein gasoline injector pulse width, then WF is one (pure water).

Alternatively, or in addition, a combination of feedback information andother information can be used to estimate WF. For example, one can usethe airflow (e.g., from the MAF sensor) and air/fuel ratio (e.g. from anexhaust sensor) to determine a total amount of fuel provided by theinjectors, and then use the injector slopes and offsets to determine anamount and ratio of water in the water/ethanol mixture.

In one embodiment, various factors may be considered, including injectortransfer functions (fuel mass flow vs. pulse width) may includecompensation for changes in specific gravity and viscosity, which can bethemselves a function of the water fraction. Thus, the water fraction(WF) may be referred to as the fraction of water in an ethanol/watermixture, although other fractions may be used, such as the fraction ofwater in the overall ethanol/water/gasoline mass. In the example wherethe water fraction is the fraction of water in an ethanol/water mixture,the following procedure may be used for calculating/estimating the waterfraction (WF) during engine operation:

-   (1) First, the method may be enabled once the system has attained    convergence about stoichiometry with feedback from one or more    exhaust gas oxygen sensor(s), using type 1 injectors only (e.g.,    gasoline injectors in this example).-   (2) Next, a turn-on pulsewidth near a minimum pulsewidth on the type    2 injectors (e.g., ethanol/water injectors in this example) may be    set. A smaller pulsewidth is desired to reduce excursions in the    air/fuel ratio when injecting an unknown, or relatively unknown    water mixture (where the mixture may be an ethanol/water mixture in    one example). The minimum pulsewidth can be the pulsewidth which    gives stable and repeatable flowrate control, and may be variable    with operating conditions. In one example, to improve accuracy in    determining a water fraction (WF), a larger pulsewidth may be used    to increase the signal to noise ratio (i.e., generate a larger    amount of water to be detected). The turn-on pulsewidth may be    determined in at least two ways: (a) mapping of representative    hardware, and determination of minimum pulsewidth for accurate WF    calculations (this may be a function of speed, load, temperature,    etc.), or (b) starting with the minimum stable pulsewidth, and    gradually increasing pulsewidth of the ethanol/water injectors    during (3) below, until the pulsewidth of the gasoline injectors    changes sufficiently to ensure an accurate WF calculation.-   (3) Next, the controller can adjust a pulsewidth of the type 1    (e.g., gasoline, in this example) injectors to regain closed-loop    stoichiometry based on exhaust oxygen sensor(s).-   (4) Then, by using the pulsewidth adjustment amount of the gasoline    injectors, the controller can calculate a mass of gasoline per    cylinder per combustion event, or fuel_mass_gas. This can be done    using a conversion that includes the injector slopes, such as    described with regard to FIG. 35.-   (5) Using the mass of gasoline from (4), the measured or inferred    air mass, and the known stoichiometric air/fuel ratios of the fuels    being combusted (e.g., gasoline and ethanol), the controller can    calculate an ethanol fraction (EF) using the equation below. The    controller can calculate the stoichiometric air/fuel ratio of the    gasoline during step (1) above, based on measured or inferred air    mass and on injector mass flow vs. pulsewidth (thus accounting for    variations due to oxygenated gasoline etc). Specifically, an example    ethanol fraction (EF) can be calculated as:

${EF} = \frac{\left( {{air\_ mass} - {{fuel\_ mass}{\_ gas}*{AF\_ stoich}{\_ gas}}} \right)}{\left( {{air\_ mass} - {{fuel\_ mass}{\_ gas}*{AF\_ stoich}{\_ gas}} + {{fuel\_ mass}{\_ gas}*{AF\_ stoich}{\_ eth}}} \right)}$

where

-   -   EF=ethanol fraction of total gasoline+ethanol (not water)    -   air_mass=mass of air per cylinder per combustion event    -   fuel_mass_gas=mass of gasoline per cylinder per combustion event    -   AF_stoich_gas=stoichiometric air/fuel for gasoline        (approximately 14.6, or from (1))    -   AF_stoich_eth=stoichiometric air/fuel for ethanol (approximately        9.0 for pure ethanol, or approximately 9.8 for E85, or from        previous closed-loop operation on ethanol similar to (1)).

-   (6) Using the mass of gasoline from (4) and the ethanol fraction    from step (5), the controller can calculate the mass of ethanol    using the equation below.    fuel_mass_ethanol=(EF*fuel_mass_gas)/(1−EF)    -   where fuel_mass_ethanol=mass of ethanol per cylinder per        combustion event.

-   (7) Using the mass of ethanol from (6) and the pulsewidth of the    ethanol/water injectors, the controller can calculate the water    fraction (WF) using one of the equations below. If the injector    characteristics (slopes) are not a function of water fraction, the    equation is:    WF=1−{fuel mass_ethanol/[(PW−OFFSET1)*ALOSL]}

where

WF=water fraction, of total ethanol+water (not gasoline in this example)

PW=pulsewidth of the ethanol/water injectors

OFFSET1=ethanol/water injector offset (initial delay) as a function ofvoltage

ALOSL=slope of ethanol/water injectors (mass per time) at low PW

If the injector characteristics (slopes) are a function of the waterfraction, the equation is:

${{- {ALOSL\_ eth}}*\left( {k - 2} \right)} - \frac{{sqrt}\begin{bmatrix}{{{{ALOSL\_ eth}\hat{}2}*{\left( {k - 2} \right)\hat{}2}} - {4*}} \\{{ALOSL\_ eth}*\left( {1 - k} \right)*} \\\begin{pmatrix}{{ALOSL\_ eth} - {{fuel\_ mass}{{\_ ethanol}/}}} \\\left( {{PW} - {{OFFSET}\; 1}} \right)\end{pmatrix}\end{bmatrix}}{2*{ALOSL\_ eth}*\left( {1 - k} \right)}$

where

ALOSL_eth=slope of ethanol/water injectors at low PW with ethanol

ALOSL_water=slope of ethanol/water injectors at low PW with water

k=ALOSL_water/ALOSL_eth

sqrt[ ]=square root of expression in brackets

While the above equations show one approach for performing thecalculations and determinations, they may be modified to includealternative fuel types, alternative injector characteristic equations(for example mass flow vs pulsewidth may be curved), etc. Further,various modifications may be made to the equations to improve accuracy,or improve simplicity of calculation, if desired.

To illustrate the source of the above equations and thus provide detailsfor modification of the equations, the relationship between the mass ofgasoline, the measured or inferred air mass, the known stoichiometricair/fuel ratios of the fuels being combusted (e.g., gasoline andethanol), and the ethanol fraction (EF) can be derived by first notingthat: fuel_mass_gas=(1−EF)*fuel_mass_total, and then manipulating thisequation to substitute for the fuel mass in terms of the air mass andoverall air-fuel ratio as:fuel_mass_gas=(1−EF)*air-mass/AF_stoich_total. Then, the individualair-fuel ratios of the fuel types can be inserted as:fuel_mass_gas=(1−EF)*air_mass/[(1−EF)*AF_stoich_gas+EF*AF_stoich_eth].From this, the equation can be rearranged to give:fuel_mass_gas*AF_stoich_gas−EF*fuel_mass_gas*AF_stoich_gas+EF*fuel_mass_gas*AF_stoich_eth=air_mass−EF*air_mass,which leads to the equation listed above in (5).

Likewise, the mass of ethanol may be derived by noting thatfuel_mass_ethanol=EF*fuel_mass_total. Then, by manipulating thisequation, the equation listed in (6) can be obtained.

Further, the water fraction (WF) can be derived (in the case where anyinteraction between WF and slope/offset changes is ignored) by startingwith the following equation 1:PW=OFFSET1+LBM _(—) INJ _(—) TOT/ALOSL  [equation 1]

where

-   -   PW=pulsewidth of the ethanol/water injectors    -   OFFSET1=ethanol/water injector offset (initial delay) vs battery        voltage    -   LBM_INJ_TOT=total mass of ethanol/water mixture injected per        cylinder per combustion event    -   ALOSL=slope of ethanol/water injectors (mass per time) at a        lower PW

Note that the water fraction determination process occurs with theethanol/water injectors at low pulsewidths, so these equations are basedon the steep part of curve with slope ALOSL (it will be apparent thatsimilar equations could easily be derived for higher pulsewidths ifdesired).

Then, using a definition of WF and rearranging to solve for LBM_INJ_TOTgives:WF=fuel_mass_water/LBM _(—) INJ _(—) TOT=(LBM_INJ_(—)TOT−fuel_mass_ethanol)/LBM _(—) INJ _(—) TOT

Note that WF is the fraction of water in the ethanol/water mixture inthis example, not the overall ethanol/water/gasoline mass, although sucha parameter may be determined and used for engine control. The equationabove can be rearranged to give equation 2:LBM _(—) INJ _(—) TOT=fuel_mass_ethanol/(1−WF)  [equation 2]

Rearranging equation 1 and substituting LBM_INJ_TOT from equation 2gives: (PW−OFFSET1)*ALOSL=fuel_mass_ethanol/(1−WF), which can berearranged to give:WF=1−{fuel_mass_ethanol/[(PW−OFFSET1)*ALOSL]}

In an alternative embodiment, the equations may be derived for the casewhere the injector slope (and/or offset) is a function of the waterfraction. In this example, the characteristics of FIG. 35 may again beutilized. As above, in one example, the water fraction determinationprocess may occur with the ethanol/water injectors at pulsewidths belowa threshold value (such as below PW_BP), and thus the followingequations can be based on the steeper part of the injector curve withslope ALOSL, although similar equations could be derived for higherpulsewidths, if desired.

In this example, it is assumed that the offset (OFFSET1) is not afunction of water fraction, because the offset is the time required toovercome inertia of the injector pintle and electrical inertia of thedriver circuit, although it may be a function of other parameters, suchas battery voltage and temperature. Assuming that the injector slopechanges linearly in proportion to the water fraction, the slope would bemeasured with pure water and with pure ethanol (or E85) and expressedas:ALOSL_total=WF*ALOSL_water+(1−WF)*ALOSL _(—) eth

where

-   -   ALOSL_water=slope of ethanol/water injectors at low PW with        water    -   ALOSL_eth=slope of ethanol/water injectors at low PW with        ethanol    -   ALOSL_total=slope of ethanol/water injectors at low PW with        ethanol/water mixture

Substituting ALOSL_total into equation 1 yields:PW=OFFSET1+LBM _(—) INJ _(—) TOT/[WF*ALOSL_water+(1−WF)*ALOSL _(—)eth]  [equation 3]

Substituting LBM_INJ_TOT from equation 2 gives:PW=OFFSET1+[fuel_mass_ethanol/(1−WF)]/[WF*ALOSL_water+(1−WF)*ALOSL _(—)eth], which can be rearranged to give:WF*WF*(ALOSL _(—) eth−ALOSL_water)+WF*(ALOSL_water−2*ALOSL _(—)eth)+ALOSL _(—) eth−fuel_mass_ethanol/(PW−OFFSET1)=0

Expressing the injector's water slope as a constant multiplied by itsethanol slope gives ALOSL_water=k*ALOSL_eth, which can then besubstituted into the previous equation as:WF*WF*(ALOSL _(—) eth−k*ALOSL _(—) eth)+WF*(k*ALOSL _(—) eth−2*ALOSL_(—) eth)+ALOSL _(—) eth−fuel_mass_ethanol/(PW−OFFSET1)=0

Solving the quadratic function yields two possible results, with thephysically meaningful solution having WF greater than or equal to zero.Further, in this example, k should be greater than one because water hasa higher density and lower viscosity than ethanol. Approximatinginjector flow with the equation for orifice flow, it becomes clear thatk may also be less than two in this example. From this, the appropriateselection of the equation for WF can be obtained, which is set forthabove herein in (7).

Referring now specifically to FIG. 24, a routine is described forestimating a water fraction using the equations noted herein. In 2410,the routine determine whether an engine start and/or refueling event inthe tank for the water (or water blend) has occurred. If so, the routinecontinues to 2412 (if not, re-calculation of WF is not necessary). In2412 the type 2 injection (e.g., water/ethanol injection) and fuel vaporpurging systems are disabled, and stoichiometry for type 1 injection(e.g. gasoline) is calculated based on measured or inferred air mass andon feedback from the exhaust gas oxygen sensor. Then the routinecontinues to 2414 to determine whether the amount and/or ratio of type 2injection is sufficient to provide accurate learning/estimation of awater fraction.

If not, the routine increases the amount and/or frequency of type 2injection in 2416 to increase sensitivity and/or accuracy of themeasurement. Further, in 2416, the routine may also purge awater/ethanol mixture through the fuel lines after a refueling event, toensure that the inferred WF reading has sufficient accuracy andcorrelation to the mixture in the tank. The purging could involvebypassing the water/ethanol fuel rail on a return fuel system. In theexample of a return-less fuel system, the WF inference process describedabove may continue for a sufficient time or number of injections toensure that the water/ethanol mixture in the fuel lines has been usedand the new mixture ratio is provided to the engine thus providingaccurate estimates. This time can be calculated from the known volume ofthe fuel line and summation of the water/ethanol used during the WFinference process, if desired. Finally, the routine continues to 2418 toupdate the estimate of WF based on the sensed information using arolling average filter, or other such filter.

While the above approaches have been described for estimating a waterfraction, various modifications and/or changes and/or additions may beused. For example, the estimation may occur at periodic intervals, orthroughout engine operation, rather than only in response to an enginestart or refueling event. Further, type 2 injection may be providedspecifically for estimation, even when not needed to reduce knock, sothat an estimate can be updated, or the estimate could be updated onlywhen type 2 injection is needed to reduce knock.

By providing an accurate estimate of the water fraction, it is possibleto provide more accurate delivery via the type 2 injection and thusprovide improved knock resistance and efficient use of the type 2resources. An example of a routine to take advantageous use of suchinformation is provided below with regard to FIG. 25.

Referring now specifically to FIG. 25, a routine is described forcontrolling engine operation based on a water fraction of anethanol/water blend in a tank provided via a direct injector or portinjector to the engine, in addition to a gasoline injector (port ordirect).

In this example, various parameters are adjusted as the water fractionin a water/ethanol blend varies. For example, the measured or inferredwater fraction may be used to control the amount of gasoline injectionand the amount of water/ethanol injection for a given set of operatingconditions. Further it may be used to adjust a desired air-fuel ratioand/or desired ethanol fraction due to changes in cooling and octaneeffects. It may be used to adjust injection pulse width of thewater/ethanol injector in order to attain the desired mass flow of waterand/or ethanol. It may also be used to limit maximum torque and/or powerand/or boost to reduce engine degradation, at least under someconditions.

The measured or inferred water fraction may also be used to varyinjection timing. In particular, if the WF is close to one, then verylate injection (during the expansion and/or exhaust stroke) can be usedto control exhaust temperature. Such an approach may be used when thereis little or no ethanol in the mixture, thus avoiding to potentialemissions (e.g. HC, aldehydes, CO, etc.) that may be produced from thelate injection of ethanol. In this way, late water injection for exhausttemperature control may be used under some conditions.

Also, on a turbocharged engine, late injection may also be used toincrease mass flow to the turbine, which may increase boost at low RPMand/or reduce turbo lag. While there may be a penalty from loweringtemperature/energy to the turbine (which may offset the benefit of addedmass flow), it may be possible to avoid or reduce this penalty byinjecting at a time when the water spray is likely to impinge on thepiston and/or cylinder walls. Such operation may avoid excessive coolingof the exhaust gas.

In 2510, the routine reads engine operating parameters, such as enginespeed, engine load, etc. Then, in 2512, the routine reads an estimatedwater fraction (WF) in an ethanol/water mixture, such as described abovewith regard to FIG. 24. Next, in 2514, the routine determines a desiredcharge cooling or knock reduction based on current operation conditions,and optionally based on feedback from a knock sensor or other sensorindicative of knock.

Then, in 2516, the routine determines a desired quantity of type 2injection based on the knock reduction needed and the water fraction.For example, as shown by FIG. 26, due to the greater charge coolingeffect of water, as the water fraction increases, a smaller quantity (orPW) of type 2 injection may be desired. Further, as the water fractionincreases, less adjustment to the type 1 injection (e.g., gasolineinjection) is needed as less combustible fuel is provided via the type 2injection, which compensation is provided via 2518 and 2520. Thesedeterminations identify how much ethanol (or ethanol blend, or anotheralcohol or alcohol blend) is provided based on the amount determined in2516, and then determine the amount of adjustment to the type 1injection. Then, in 2522, the routine determines injection timings forthe type 2 injection based on the water fraction and the value from2516. Finally, the PW limits are checked in 2524 and adjustments aremade if necessary, as described herein above.

Various advantages may be achieved by such operation. In one example, itis possible to use knowledge of the water fraction to provide a correctamount of charge cooling to reduce knock, even when the water fractionis changing. Further, it is possible to maintain accurate engineair-fuel ratio control and torque output by compensating for variabilityin water fraction by appropriate adjustment of the type 1 fuel injectorbased on the water fraction.

In this way, it is possible to use water injection, or a blend of waterinjection, to increase compression ratio and/or boost pressure due todecreased knock at high loads, while also compensating for variabilityin the water fraction and alcohol (e.g., ethanol) fraction of themixture. Further, a vehicle customer is able to achieve improved engineoperation using one or both of water and an alcohol based fuel as asecondary injection in the engine. Further still, late injection forexhaust temperature control and/or increased boost at low RPM and/orreduced turbo lag can be provided with water injection, for exampledirectly injected water or water blend.

As noted above, FIG. 26 shows the amount of type 2 injection for a givencharge cooling amount. Note that while a linear curve is shown, this isjust one example, and the curve may be nonlinear. Also note that this isjust one curve shown for a single desired amount of charge cooling. Adifferent curve may be used for each amount of charge cooling, providinga family of curves, as shown in FIG. 27.

Referring now to FIG. 28, a routine is described for reacting to anindication of engine knock, such as from a knock sensor, cylinderpressure sensor, or other indication that knock is occurring, or isabout to occur. In 2810 the routine reads current operating conditions,such as speed, load, etc. Then, in 2812, the routine determines whethera measure of knock from knock sensor 182 has reached a threshold valuethus providing an indication of knock. As noted above, various otherindications may be used, if desired.

If knock is indicated in 2812, the routine continues to 2814 todetermine whether type 2 injection is enabled and whether additionaltype 2 injection/fueling is feasible. In other words, the routinedetermines whether conditions are acceptable to use any type 2injection, such as, for example, coolant temperature, whether type 2fuel is depleted, and various others as noted herein, and whether type 2pulsewidth is less than maximum. If not, the routine proceeds to 2816 toretard spark timing to reduce knock, and then takes additional actionsin 2818, optionally, if necessary, such as reducing airflow, etc.

If the answer to 2814 is yes, the routine proceeds to 2820 to increasetype 2 injection (e.g., ethanol injection) and correspondingly decreasetype 1 injection to reduce a tendency for knock, assuming that it ispossible to increase type 2 injection and/or decrease type 1 fuelinjection. Alternatively, the desired ethanol fraction (EF) may beincreased to increase a relative amount of ethanol to gasoline, assumingit is possible to further increase the fraction. In other words, resortto spark retard and other operations as noted herein to reduce knock maybe used if type 2 injection is near a maximum available amount. Thus,spark may optionally be retarded relative to its current timing beforeor concurrently with the type 2 injection increase in 2822, and thenreturned once the fuel adjustments have been effective. Note that thecombination of spark timing and fuel adjustment may be beneficial inthat the spark timing change may have a faster response on knock thanthe fuel change under some conditions. However, once the fuel adjustmenthas been effected, the spark timing may be returned to avoid fueleconomy losses. In this way, fast response and low losses can beachieved. Under other conditions, only spark adjustments, or fueladjustments without spark adjustments may be used so that even temporaryretard of spark timing is reduced.

Various examples of such alternative operation are shown in the graphsof FIG. 29, which show an indication of knock in the top graph (wherethe dashed line is a limit above which knock is identified, where thethreshold may be variable with operating conditions), spark timingrelative to a reference (dashed line) in the second graph, type 1injection amount (e.g., port fuel amount) in the third graph, and type 2injection amount (e.g., direct cylinder alcohol containing fuel amount)in the bottom graph.

In this example, at time t1 an indication of knock rises above athreshold value and the spark timing is retarded while the type 1 andtype 2 injection amounts are also adjusted. In this case, the fueladjustments are offsetting in direction and of different amounts toaccount for the different power density and stoichiometric air-fuelratio between the fuel types. The spark timing is than returned to avoidfurther fuel economy losses.

Then, at t2, the engine output torque is gradually increased byincreasing airflow and respective fuel amounts until at t3, anindication of knock is again generated. At t3, the routine adjusts type1 and type 2 injection amounts without additional spark retard to reduceknock, while still increasing the total fuel injection energy. Then,fuel injections and airflow increases, and then decreases until at timet4 knock again reaches a threshold value. At this point, spark timing isretarded until t5, at which point the fuel injection amounts areadjusted, while still continuing to reduce the total amount of fuelenergy. At t5, the effect of the relative fuel adjustment between thefuel types takes effect and the spark timing may be gradually returnedto its desired position to avoid further fuel economy losses fromretarded ignition timing.

In this way, it is possible to provide varying levels of total fuelinjection amounts, while varying the relative amounts of fuel types andignition timing to reduce knock.

Referring now to FIG. 30, an alternative engine starting routine isdescribed that may be used. In this example, the routine controls fuelinjection type, and amount, based on a fueled cylinder event strategy.Various methods may be used to identify a cylinder event, such as bydecoding engine position based on cam sensor and crank sensor signals. Acylinder event signal identifies when a given engine cylinder reachestop-dead-center of compression stroke, in one example. Alternatively,other cylinder events may be used.

In step 3010, engine operating conditions are read. Measured or inferredoperating conditions such as engine coolant temperature, catalysttemperature, time since engine last operated (soak time), and otherparameters may be used. These parameters may be used to compensate theengine fuel request in 3024, described below. These parameters caninfluence engine operation in different ways depending on their state.For example, low engine coolant temperatures may lead to air-fuelenrichment, but normal engine coolant temperatures may lead tostoichiometric air-fuel.

In 3012, the routine decides to proceed based on whether the engine isrotating. If the engine is not rotating, the routine waits until a crankposition sensor detects engine rotation. If the engine is rotating, theroutine proceeds to 3014. In 3014, the controller determines if acylinder event has occurred, if so, the routine proceeds to step 3016.If no new cylinder events have occurred, the routine waits until acylinder event is observed. In step 3016, the routine determines ifsynchronization between controller 12 and engine 10 has occurred.Synchronization can occur when engine timing is aligned with enginecontroller operation. If synchronization has occurred, the routineproceeds to step 3018, if not, the routine proceeds to step 3020.

In 3018, the number of fueled cylinder events is incremented since acylinder event has been detected and the engine and controller 12 are insynchronization, thus indicating that fuel delivery may occur. Thenumber of fueled cylinder events may then be used to determine an amountof fuel to be delivered to the cylinder or cylinders currently beingfueled. Further, as noted below, is may also be used to select wherefuel is delivered and/or a type of fuel delivered and/or when during acycle fuel is delivered. For example, injection timing may be variedbased on a number of fueled cylinder events. Likewise, a selection oftype 1 and/or type 2 fuel may be based on a number of fueled cylinderevents as noted in 3023 below. Further, a selection of a desiredair/fuel ratio (or relative air-fuel ratio) may be based on a number offueled cylinder events.

Note that alternatively to, or in addition to a number of fueledcylinder events, a number of combustion cylinder events and/or otherfactors may be used.

Continuing with FIG. 30, in 3020, the routine observes cam and cranksignals that allow determination of engine position. When engineposition is established, engine controller 12 aligns operations, sparkand fuel delivery, to engine timing, becoming synchronized. Fueldelivery may be suspended until synchronization occurs in this example.Upon synchronization the fueled cylinder event counter is set to zeroand the routine continues to 3022 where an engine air amount predictionis retrieved from an engine air amount algorithm. Alternatively, a massair flow meter may be used to determine the engine air amount. Byintegrating the air mass signal over a cylinder event and thenpredicting future engine air amounts by extrapolation, using previousengine air amounts, a predicted engine air amount can be calculated.

In 3023, the routine selects a fuel type based on the number of fueledcylinder events. For example, where different fuels are injected (e.g.,port gasoline and direct injection ethanol), a port injector may be usedto inject gasoline into each cylinder on an event basis (i.e., eachcylinder has a unique amount of fuel injected based on the combustionevent number). After a predetermined number of events, inferred cylindertemperature, time, and/or other factors, the engine could betransitioned over to direct injection. For example, both injection typesmay be enabled after a selected number of events, or only directinjection may be used after a selected number of events.

In 3024, a desired air-fuel ratio for the up coming fueled cylinderevent is determined based on a number of fueled cylinder events andother factors, such as coolant temperature, etc.

In 3026, individual cylinder fuel mass is calculated based on thedesired air-fuel ratio calculated in 3024, predicted engine air amountretrieved from 3022, and the fuel type selected in 3023. If two fueltypes are selected, the calculation for each fuel type is performed byfurther using a desired ratio or fraction of fuel types, which may be afunction of engine speed, load, and/or other operating parameters.Further, other modifications may be used based on fuel puddle dynamicsfor any fuel injected via a port injector.

In 3028, the fuel pulse width(s) is(are) determined from the calculatedfuel mass(es) and a function that represents the time to deliver a givenfuel mass, and the respective injector slopes/offsets. The routine thencontinues on to 3030 where injectors are activated to deliver thedesired fuel masses. The routine then advances to 3032. In 3032, theroutine passes the fueled cylinder event number to a spark deliveryroutine that can adjust spark based on the fueled cylinder event numberand cylinder burn rate. Typically, desired spark is advanced if the burnrate is slower and retarded if the burn rate is faster. The burn ratemay be determined by the cylinder design and type of fuel, e.g.,gasoline, ethanol, methanol, or blend. Base spark timing is retrievedfrom predetermined values stored in a table. The base spark table has xindices of engine coolant temperature and y indices of fueled cylinderevents. If the burn rate of the fuel being used changes, a functionFNBUR_SPK, alters the spark demand by adding an offset to the basespark. FNBUR_SPK is empirically determined and outputs spark offset as afunction of burn rate. As the burn rate changes, depending on the fueltype, spark is advanced or retarded appropriately. In other words, thebase spark angle that is based on the number of fueled cylinder eventsis modified based on cylinder burn rate. By linking spark angle tocylinder burn rate and fueled cylinder events, engine emissions can bereduced on a variety of fuel types. The routine then continues to 3034.

In 3034, engine operating conditions are evaluated to determine ifclosed loop fuel control is desired. Common signals used to determinedesired closed loop engine operation include; time since start, exhaustgas sensor temperature, engine coolant temperature, and engine load. Ifclosed loop fuel control is desired the routine proceeds to 3036 wherefuel control transitions from open loop control to closed loop controlby ramping fuel toward the desired air-fuel ratio, which may bestoichiometry. If closed loop fuel control is not desired the routineexits until it is called again to determine fuel for the next cylinder.Closed loop control may be executed as described above herein.

Alternatively, another embodiment delivers fuel based on the number offueled cylinder events then transitions to time based fuel delivery.This method benefits from the advantages of fueling based on the numberof fueled cylinder events during starting then reduces computations byusing time based fueling. In another alternative, simultaneous use offueled cylinder event based and time based fueling is provided. Eventbased fueling offers the before-mentioned advantages. Time based fuelingpermits simplified calibration of fuel compensation for slower changingconditions, such as fuel vaporization. By using both methods, fuelamount can be compensated for both engine conditions that change slowlyand engine conditions that change rapidly.

In still another embodiment, non-sequential fueling may also be used onan event basis.

The above routine can achieve various advantages since the routine canprovide selective fuel delivery on an individual cylinder basis. Bydetermining individual cylinder fuel amounts and types, individualcylinder mixtures and combustion may be better controlled.

Referring now to FIGS. 31-34, routines for controlling and adapting tofuel vapor purging as well as injector and airflow sensor errors isdescribed. Specifically, in FIG. 31, a routine for controlling a singlesource (e.g., valve) of fuel vapors (such as shown in FIG. 8 or 10, forexample), which may be from one or more tanks or storage canisters, isdescribed. Specifically, in 3110, the routine determines whether fuelvapor purging is requested. The request may be based on variousoperating conditions, such as speed, load, temperature, etc. Next, in3112, the routine adjusts a purge valve to provide a desired amount offlow into the intake manifold. The desired amount of flow may includegradually ramping the flow up when first enabling purging, and varyingthe flow with operating conditions, such as speed and load, for example.

In 3114, the routine adjusts fuel injection from one or more injectorsper cylinder based on feedback from exhaust gas oxygen sensors tomaintain a desired air-fuel ratio. In addition, compensation based on afeedforward estimate of vapors in the purge flow may be used, ifdesired. The adjustment of fuel injection may utilize various types ofair-fuel ratio control, such as, for example, the approach describedherein with respect to FIG. 11. The approach may include injectorselection based on various additional factors, such as whether injectorsare active, or based on a content of vapors in the purge flow, asdescribed in more detail with regard to FIG. 33. Further, the selectionmay be based on minimum and/maximum injector pulsewidth values, as wellas other operating conditions. In one embodiment, a port injectorinjecting gasoline may be adjusted as purge flow and/or concentrationvaries. In another embodiment, a direct injector injecting a mixturecontaining an alcohol may be adjusted as purge flow and/or concentrationvaries. In still another embodiment, combinations of variation of bothport and direct injectors may be used.

Continuing with FIG. 31, in 3116 the routine learns a vaporconcentration and/or composition in the purge flow, and then learns fuelinjector(s) and air meter aging values, as described herein with regardto FIG. 34.

In this way, it is possible to provide robust compensation for fuelvapor purging even when the content of the vapor varies, while stillmaintaining a desired overall amount of fuel types during combustion.For example, where the vapor may contain varying amounts of gasoline andethanol, the routine can appropriately use compensation of gasoline andethanol injection to maintain desired total amount of combustiongasoline and ethanol under varying operating conditions. Further, it ispossible to provide compensation even when one fuel type is depleted ornot enabled during the current operating conditions, thus providingimproved opportunity to purge fuel vapors.

Referring now to FIG. 32, a routine similar to that of FIG. 31 isdescribed, except that more than one purge control valve may beprovided. In this specific example, two valves are provided. In oneexample, the valves can control vapors from different fuel sources, suchas shown with regard to FIG. 9. First, in 3210, the routine determineswhether fuel vapor purging is requested. The request may be based onvarious operating conditions, such as speed, load, temperature, etc.Next, in 3212, the routine selects a number of active purge valves to beoperated. For example, under some conditions, a first valve may be usedto enable fuel vapor purging of only a first fuel type, and under otherconditions, a second valve may be used to enable fuel vapor purging ofonly a second fuel type. These conditions may include the amount ofvapors generated in the respective systems, temperature, speed, load,desired ethanol fraction, or others. In another example, the routine mayenable purging of from both valves during common operating conditions,and concurrently with each other. Thus, in 3214, the routine determineswhether single purge valve operation, or multiple purge valve operation,is selected.

If single operation is selected, the routine continues to 3216 to selectwhich valve should be active. For example, purging from different valvesmay alternatively be activated so that both systems are able to purgefuel vapors. The relative amounts and durations of activation can bevaried with operating conditions and/or with desired ethanol fraction.For example, purging from the ethanol system may be preferred whenhigher ethanol fraction is desired. Also, systems having highervolatility fuels may need additional amounts of purging (such as greaterflows, longer durations, etc.). Next, in 3218, the routine adjusts theselected purge valve to provide a desired flow amount.

Alternatively, if dual purge valve operation is selected, the routinecontinues to 3220 to adjust a first purge valve to provide a firstdesired flow amount, and then to 3222 to adjust a second purge valve toprovide a second desired flow amount. Then, from either 3222 or 3218,the routine continues to 3224 to adjust fuel injection of one or morefuel injectors per cylinder to compensate for the fuel vapors based onexhaust gas oxygen sensor feedback and optionally feedforward estimates.As noted above, such operation may include selection and variation ofwhich injector provides adjustment based on operating conditions, aswell as selection criteria described with regard to FIG. 11 and FIG. 33.

Continuing with FIG. 32, in 3226 the routine learns a vaporconcentration and/or composition in the purge flow, and then learns fuelinjector(s) and air meter aging values in 3228, as described herein withregard to FIG. 34.

In this way, it is possible to provide robust compensation for fuelvapor purging even when the content of the vapor varies, while stillmaintaining a desired overall amount of fuel types during combustion.For example, where the vapor may contain varying amounts of gasoline andethanol, the routine can appropriately use compensation of gasoline andethanol injection to maintain desired total amount of combustiongasoline and ethanol under varying operating conditions. Further, it ispossible to provide compensation even when one fuel type is depleted ornot enabled during the current operating conditions, thus providingimproved opportunity to purge fuel vapors. Finally, it is possible toprovide desired purging of more than one fuel type.

Referring now to FIG. 33, a routine is described for selecting injectorsto provide compensation for fuel vapor purging from one or more fuelvapor purge control valves and/or one or more fuel types contain in fuelvapors. In this example, the routine selects one or more injectors percylinder to provide adjustment to fuel vapors based on content of thevapors, as well as other factors, to maintain a desired air-fuel ratio.In one embodiment, such operation provides an ability to maintain adesired overall relative amount or ratio of different fuel types.Specifically, in 3310, the routine determines whether fuel vapor purgecompensation is enabled. If so, the routine continues to 3312 todetermine whether compensation for type 1 fuel contained in the purgeflow is requested. In one embodiment, the routine determines whethertype 1 fuel is contained in the vapors being purged into the engine. Ifso, the routine continues to 3314 to determine whether type 1 injectionis enabled at the current conditions. If so, the routine adjusts type 1injection to compensate for type 1 fuel in the fuel vapors based onfeedback from exhaust gas oxygen sensors and possibly using feedforwardestimates of vapor contents in 3316. In this way, an increase in type 1fuel attributed to fuel vapor purge can be compensated by acorresponding decrease in type 1 fuel injected into the cylinder, thusprovide accurate air-fuel control and maintenance of a desired amount oftype 1 fuel at the given operating conditions.

Alternatively, when the answer to 3314 is no, the routine continues to3318 to adjusts type 2 injection to compensate for type 1 fuel in thefuel vapors based on feedback from exhaust gas oxygen sensors andpossibly using feedforward estimates of vapor contents. While this mayvary the amount of fuel types in the cylinder, it is still possible tomaintain a desired air-fuel ratio, and thus improve emission controleven when type 1 fuel injection may be disabled, such as due todegradation.

The routine then continues from either 3316 or 3318 or a NO in 3312 to3320. In 3320, the routine determines whether compensation for type 2fuel contained in the purge flow is requested. In one embodiment, theroutine determines whether type 2 fuel is contained in the vapors beingpurged into the engine. If so, the routine continues to 3322 todetermine whether type 2 injection is enabled at the current conditions.If so, the routine adjusts type 2 injection to compensate for type 2fuel in the fuel vapors based on feedback from exhaust gas oxygensensors and possibly using feedforward estimates of vapor contents in3324. In this way, an increase in type 2 fuel attributed to fuel vaporpurge can be compensated by a corresponding decrease in type 2 fuelinjected into the cylinder, thus providing accurate air-fuel control andmaintenance of a desired amount of type 2 fuel at the given operatingconditions.

Alternatively, when the answer to 3322 is no, the routine continues to3326 to adjust type 1 injection to compensate for type 2 fuel in thefuel vapors based on feedback from exhaust gas oxygen sensors andpossibly using feedforward estimates of vapor contents. While this mayvary the amount of fuel types in the cylinder, it is still possible tomaintain a desired air-fuel ratio, and thus improve emission controleven when type 2 injection may be disabled, such as due to degradation.

Note that in an alternative embodiment, the routine may vary differentfuel injector amounts for a cylinder based on the type of vapors beingpurged and/or based on a quantity of types of vapors being purged.

Referring now to FIG. 34, a routine is described for adaptively learningcorrections in the air and fuel metering system, such as fuel injectorcorrections, for system configurations having multiple fuel injectorsper cylinder, such as the various examples described herein, or forsystems having multiple fuel metering devices for different fuel types,such as FIG. 36 or 37, for example.

In one particular embodiment where one injection type is a fuel such asgasoline (which may be port or directly injected) and a second injectiontype includes an alcohol containing fuel (such as ethanol, or an ethanolblend, which may be port or directly injected), a method is providedthat takes advantage of regression techniques to independently determinethe characteristics of the elements of the air and fuel metering system.In one example, a routine may be used that schedules the injection oftype 2 injection as a function of an engine parameter, such as air massor load, and then learns an air and fuel correction as a function ofthat engine parameter. Thus, if the injection of alcohol via thein-cylinder injectors is scheduled strictly as a function of air mass,an adaptive system that determines an air fuel correction as a functionof air mass may be used to correct for an air fuel error from a systemwith air meter errors (slope) and primary and secondary injector errors(slope and offset).

However, if the amount of type 2 injection varies with other parameters,such as in response to temperature and/or knock sensor feedback orexhaust gas oxygen sensor feedback, an alternative approach may be used.Specifically, in this example, the approach described in U.S. Pat. No.6,138,655 (which is incorporated herein by reference) may be adapted andmodified. The method may include air mass squared and purge volumesquared terms based on vehicle experience. Further, different algorithmsmay be used, such as the Potters Square Root algorithm or the RecursiveLeast Squares algorithm depending on numerical stability issues.

In particular, by determining the coefficients of the followingequation, improved adaptive learning of air and fuel errors may beachieved:FuelCorrection=α₀+α₁*AirMass+α₂*AirMass²+α₃ *RPM+α ₄*PurgeVolume+α₅*Purge Volume²+α₆*SecondaryInjector Pulsewidth

Where “SecondaryInjector Pulsewidth” refers to pulsewidth of a type 2injector, for example. The coefficient in this term would be updatedonly when the secondary injection is active using a series of linerregressions that can be separately enabled. Alternatively, rather thanusing pulsewidth, secondary injector flow may also be used. Also it maybe advantageous to add terms such as secondary injector flow orpulsewidth squared and/or secondary injections per minute to account fornon-linearities such as errors in the injector offset. Further, in stillanother alternative, the air mass and air mass squared terms may bereplaced with type 1 fuel flow and type 1 fuel flow squared. Thus, in analternative approach, the following may be used:FuelCorrection=A ₁ +A ₂*PrimaryFuelFlow+A₃*PrimaryFuelFlow² +A ₄ *RPM+A₅*SecondaryFuelFlow+A ₆*Purge Volume

Referring now to FIG. 34, a routine describes one example embodiment foradaptively learning errors.

First, in 3440, the routine determines whether the vehicle is operatingunder near steady state conditions, such as based on a rate of change ofengine speed, vehicle speed, pedal position, fuel flow, injectorpulsewidth(s), throttle position, or combinations thereof. For example,if the variation in input parameters is below an acceptable level (e.g.,engine speed, fuel flow), updates to the coefficients related to speedand fuel flow may have increased error. Therefore, in steady state, theroutine proceeds to 3432. If enough activity is present (driven bytransient operating conditions), the routine proceeds to 3412. In 3412,the routine determines whether sufficient time has passed to perform anupdate. In this way, it is possible to provide the opportunity to slowdown or speed up the adaptive routine by only providing a pre-determineddelay between coefficient updates. If it is not yet time to performupdates to the parameters, the routine jumps to step 3432. Otherwise,continue to 3414.

In 3414, the routine updates adaptive coefficients b1, b2, b3, and b4using a regression in the equation:FuelErr=b1+b2*PriFuel+b3*PriFuel^2+b4*RPM

where: FuelErr is the difference between the commanded fuel flow and“measured” fuel flow (equal to measured air flow divided by the air fuelratio measured in the exhaust); PriFul is the commanded fuel to beinjected by the primary injectors—for example, gasoline injected intothe intake ports; PriFul^2 equals PriFul squared; and RPM is themeasured engine speed.

One method that could be used to perform the regression is the commonlyknown “recursive least squares” method. Alternatively, “Potters squareroot” algorithm may also be used. Having completed the update of thecoefficients, the routine continues to 3416 to determine if thesecondary injection (e.g. in cylinder injection of alcohol or an ethanolblend, for example) is active or has been active recently. In thisexample, a regression of secondary injection data is not enabled untilthe secondary injection has been enabled, or was recently enabled. Oncesecondary injection is disabled, the routine may continue the regressionfor a short, predetermined, time to collect data at zero or lowsecondary fuel flow. Thus, if the secondary injection is not active, theroutine continues to 3430. Otherwise, the routine continues to 3418.

The following acts performed by the routine are directed to determiningthe coefficients of the fuel correction equation described herein.However, since portions of this regression may only be performed atcertain times, or under selected conditions, (e.g., when sufficientmodulation of the independent variables (primary and secondary fuelflow, engine speed, purge flow, or others) is available), the regressionmay be performed via a series of regressions of the various terms. Also,regarding determination of the terms related to the secondary injection,in one approach it may be advantages to independently control thesecondary injection from the above parameters, e.g., by selecting valuesthat were statistically independent of the engine speed and primary fuelflow or others. However, the secondary flow may be based on one or moreof these parameters to provide the desired engine response. As a result,there is the potential for some degree of correlation between thesecondary injection and these terms. Therefore, in one approach, it maybe beneficial to determine how the secondary injection correlates withthe terms, and subtract the correlated, and already compensated for,effects of secondary injection. To do this a similar approach as usedabove in 3414 may be used to update the coefficients of the equation:SecInj=c1+c2*PriFul+c3*PriFul^2+c4*RPM

where: SecInj is the commanded secondary fuel flow; and c1, c2, c3, andc4 are the coefficients being updated. Further, since some of the saneindependent variables are being used again, some of the intermediatematrices calculated for recursive least squares or Potters square rootalgorithm may be used from above and may not need to be re-calculated.

Having determined the coefficients for the correlated secondary fuelflow in 3418, in 3420 the routine determines how much of the currentsecondary fuel flow, at the current operating conditions, has alreadybeen accounted by applying those coefficients. Subtracting thecorrelated secondary fuel flow from the actual secondary fuel flow instep 3422 gives the secondary fuel flow residuals that may be used in3428.

In 3424, the routine determines how much of the fuel error has alreadybeen accounted for by the regression in 3414 by using the updated valuesof the coefficients b1 through b4 and the current operating conditions.In 3426, the routine determines the unaccounted for fuel error (fuelerror residuals) that are available for the regression in 3428. In 3428,the routine updates the coefficient for the equation:FuelResid=d*SecFIResid

where: FulResid is the residual fuel error calculated in 3426;SecFlResid is the residual secondary fuel from step 3422; and d is thecoefficient to be determined. A similar approach as in 3414 may be used,with a different independent variable, and thus previous intermediatematrices are not re-used.

It may be advantageous to expand the regression performed in 3428 toinclude additional terms such as secondary fuel flow squared to accountfor nonlinearities in the secondary fuel flow error. In this case theequation and coefficients to be updated could be of the form:FuelResid=d1*SecFlResid+d2*SecFlResid^2

Where: SecFlResid^2 is the secondary fuel residuals squared.

Having determined the correlation between fuel errors, primary andsecondary fuel flow, and engine speed, the routine now combines theterms from the previous regressions in step 3430 as follows:e1=b1−(c1*d)e2=b2−(c2*d)e3=b3−(c3*d)e4=b4−(c4*d)e5=d

to get the coefficients for the equation that describes the expectedfuel error without considering the effects of carbon canister purge:FulNoP=e1+e2*PriFul+e3*PriFul^2+e4*RPM+e5*SecInj

This equation is used in step 3434, and the coefficients are again usedin 3456.

Again, the routine updates coefficients for an equation if theindependent variables are significantly changing. For carbon canisterpurge, however, it once it has been enabled and stabilized from theinitial opening, the flow may be modulated to improve regressionresults, if desired. For example, it may be modulated independently fromvariable such as injector flow, speed, etc.

Continuing with FIG. 34, the routine determines at 3432 whether thepurge flow has been enabled and is currently being modulated. If thepurge has not yet been enabled (e.g. following a cold start), theroutine proceeds to 3456. Otherwise, the routine continues to 3434through 3454 to determine how the carbon canister purge is contributingto the measured fuel flow errors.

In 3434, the routine determines how much of the fuel error has alreadybeen accounted for above. Then, in 3436, the routine determines theresidual fuel errors that may be caused by the canister purge flow.Next, in 3438, 3440, and 3442, the routine determines how the canisterpurge correlates to the primary fuel flow and engine speed andcalculates the residual (unaccounted for) canister purge. These stepsare similar to some above and thus may re-use some intermediatecalculations, if desired.

If secondary injection has been active, the routine also determines howthe canister purge correlates to the secondary fuel flow, where thedecision to make this determination is made in step 3444. Next, in 3446,the routine performs correlation between the purge residuals and thesecondary fuel flow residuals to update coefficient g. If, in 3428, aregression with an additional term such as secondary fuel flow squaredwas used, this term would also be included here. Again, since the inputsto the regression are similar to those in 3428, some intermediate valuesused in the regression can be reused. If secondary injection is notactive, the routine proceeds to 3446, and in either case, to 3448.

In 3448, the routine combines the coefficients related to the canisterpurge flow using the technique to arrive at the equation used in 3450:CorPgVol2=h1+h2*PriFul+h3*PriFul^2+h4*RPM+h5*SecInj

This equation gives the purge volume that correlates to, and has alreadybeen accounted for, in the regressions from steps 3414 through 3430.

Continuing with FIG. 34, in 3450 through 3454, the routine determineshow the fuel error residuals correlate to the canister purge flowresiduals in a manner similar to that above. Again, it may beadvantageous to add a purge volume squared term to the regression, undersome examples. This term would account for changes in the fuel contentof the purge flow as the purge flow changes and may also tend to accountfor errors in the estimated purge flow that are likely at low purge flowrates.

Having determined the effects of the various independent parameters inthe above series of regressions, at 3456, the routine combines thecoefficients to determine the final fuel correction equation used instep 3458. The coefficients are combined as follows:A1=e1−(h1*d)A2=e2−(h2*d)A3=e3−(h3*d)A4=e4−(h4*d)A5=e5−(h5*I)A6=I

to provide the final fuel correction equation:Correction=A1+A2*PortFul+A3*PortFul^2+A4*RPM+A5*SecInj+A6*PrgVol

This compensation may then be used to modify the injected fuel flow, forexample, as described herein.

Note that in the above algorithm using a Potters Square Root Algorithm,it may be executed where values for the algorithm coefficients may bestored in memory. The values stored can be predetermined initial valuesthat are used when the computer keep-alive memory has been reset, orwill be the values updated in the last iteration of this algorithm.

Referring now to FIG. 35, a graph is shown of an example injectortransfer function, illustrating a relationship between fuel mass perinjector pulse and pulsewidth (PW). The graph shows an example two-slopeapproximation, changing at a breakpoint (BP).

Referring now to FIG. 36, an example fuel delivery system is shown foran example with a single injector per cylinder may be employed, wherethe single injector may be a direct injector or a port injector. In thisexample, a first fuel tank 3610 and a second fuel tank 3612 are shownfor holding a first and second fuel type, such as gasoline and analcohol blend. Each fuel tank has an internal fuel pump (3614 and 3616,respectively), although an external pump may also be used, or a dualpump system may be used. Each fuel tank leads to a mixing valve 3620that may be adjusted via controller 12 to vary a relative amount of eachof the fuel types, from only type 1 to only type 2, and any relativeamount in between. The mixing/control valve leads to a fuel rail 3630having one or more fuel injectors 3626 coupled thereto. In this way, arelative amount of fuel types may be delivered to the engine withoutrequiring two fuel injectors.

Referring now to FIG. 37, an alternative embodiment is shown of a fueldelivery system in which two fuel tanks are used with a fuel pump and asingle injector per cylinder, to further reduce system cost. In thisexample, fuel tanks 3710 and 3712 (each storing a respective fuel typesuch as gasoline and an ethanol or alcohol mixture) leads tomixing/control valve 3720 via respective one way valves 3722 and 3724,which may optionally be included to reduce any backflow. Then, valve3720, leads to a pump 3740 and then to fuel rail 3730 having one or moreinjectors 3736. Again, a multi-stage pump, or multiple pumps may be usedto further boost pressure, with each pump compressing a mixture of thefuel types.

Referring now to FIG. 38, an alternative embodiment is shown of a fueldelivery system in which two fuel tanks are used with fuel pumps and twoinjectors per cylinder, to provide flexibility in delivering fuel typesvia different injectors. For example, one injector may be a directinjector for a cylinder, and the other injector may be a port injectorfor the cylinder, or they may both be port or direct injectors for thesame cylinder, with different targeting, spray patterns, etc.

In this example, fuel tanks 3810 and 3812 (each storing a respectivefuel type such as gasoline and an ethanol or alcohol mixture) are eachcoupled to a first and second fuel pump 3830 and 3832 via a set of threecontrollable/mixing valves 3820, 3822, and 3824. Specifically, valve3820 is coupled directly to tank 3810 and valve 3824 is coupled directlyto tank 3812. Each of these valves may lead through an optional one waycheck valve (3826 and 3828, respectively) to respective pumps 3830 and3832. A line between the two pumps may be controlled via valve 3822,which may be used instead of or in addition to valves 3820 and 3824.Each of the pumps leads to a respective fuel rail 3834 or 3836, havingone or more fuel injectors 3840 and 3842, respectively. In one example,tank 3810 holds type 1 fuel and injector 3840 is a port injector, andtank 3812 holds a type 2 fuel, and injector 3842 is a direct cylinderinjector for the same cylinder as injector 3840.

This example configuration can enable either fuel type to be fed toether injector, or combinations of fuel types to either injector. Also,the control valves can be located upstream of the pumps so that one candeliver either fuel at either pressure, in the case where the pumpsgenerate different fuel pressures. Note, however, that the valves may belocated downstream of the pumps if the fuel pumps generated similarpressures/flows, which could be either a high pressure fuel system or alow pressure fuel system.

In one example, valve 3820 may be closed, and valves 3822 and 3824 opento allow flow from tank 3812 to both pumps/injectors. Alternatively, allvalves could be open, where the relative amounts of each valve areadjusted to vary an amount of different fuel types to differentinjectors, where the valves may be adjusted based on operatingconditions, whether fuels are enabled, etc. In this way, improvedoperation may be achieved by tailoring the fuel types and relativeamounts to different injectors for different operating conditions. Inanother embodiment, valves 3820 and 3824 may be omitted, and both tanksmay be coupled to the inlet of valve 3822, thus allowing control ofrelative amounts of fuel types to both injection systems (although onlyone injection system may be operating at any given time).

However, with the operation of the example systems of FIGS. 36-38,relative fuel amount adjustment response to conditions, such as knock,may be slower since it takes time for fuel to travel from the valve tothe injectors for delivery. Thus, in the case where adjustments in theamounts, or relative amounts, of fuel types are used to reduce knock, itmay be advantageous to first utilize spark retard and/or airflow controland/or boost control in response to engine knock. Then, once anadjustment to a relative amount of fuel types is made and takes effectin the combustion chamber, the spark retard and/or airflow controland/or boost control may be reduced so that improved fuel economy and/orperformance may be achieved, while still reducing knock via appropriateadjustment of relative amounts of fuel types, such as increased ethanolinjection.

Referring now to FIG. 39, a routine is described for managing atransition when first providing type 2 injection (e.g., ethanol) in viewof minimum pulse width operation of fuel injectors. Specifically, in3910 the routine identifies a request of activation or commencing oftype 2 fuel (e.g., via a second injector in a cylinder) based on ademand as determined by FIG. 16, for example. If such a request ispresent, the routine continues to 3912 to turn on a type 2 injector to apulsewidth at or greater than a minimum pulsewidth required for stableand repeatable operation, which may be identified by an amount Δ1. Then,in 3914, the routine reduces type 1 injection by an amount (Δ2) tomaintain an overall stoichiometric ratio. The size of Δ2 may calculatedbased on Δ1, the first and second injector characteristics (e.g.,slopes, offsets), and the stoichiometric air-fuel ratio of the type 1and type 2 fuels, as described for FIG. 23. For example, where the type1 fuel is gasoline and the type 2 fuel is ethanol, the amount of totalmass reduction in gasoline is smaller than the size of the mass increasein ethanol due to the differential stoichiometric ratios.

Note that the above adjustments are described for two injectors in asingle cylinder, however for a multi-cylinder engine, each cylinder maybe transitioned in a similar way in sequence. Also, in another example,only one or a subset of the cylinders may be transitioned to operatewith both fuel types. Further, the transition may be serial, or allcylinders may be transitioned at substantially the same time.

Further note that the above approach assumes that the relative powerdensity in the fuels compensates for the change in total fuel mass beingprovided. In other words, when increasing the type 2 injector by Δ2 anddecreasing the type 1 fuel by a smaller Δ1 so that an appropriate amountof fuel is provided to burn with the already present air, the overalltorque of the combustion may change due to power density differences inthe fuels. As the ratio of the stoichiometric air-fuel ratios betweenethanol and gasoline is similar to the ratio of power densities, only anegligible torque disturbance may be present. However, in some cases,such a torque disturbance may be perceptible. Thus, in 3918, the routinedetermines whether additional compensation may be used. If so, theroutine proceeds to 3920 to use spark and/or throttle and/or boostadjustments to compensate for such torque variation. In one example, ifthe overall torque after the transition may increase, spark retard maybe used commensurate with the change in fuel amounts, and then graduallyramped out as the throttle and/or boost level is ramped to decreaseairflow. In another example, if the overall torque after the transitionmay decrease, spark retard along with increasing airflow before thetransition may be used and then the spark retard may be removedcommensurate with the change in fuel amounts.

If the answer to 3918 is no, the routine continues to 3922 to compensatefor the effect of changing the relative amounts of fuel types on optimalignition timing. In other words, by adding type 2 fuel, it may bepossible to advance ignition timing without incurring engine knock, thusproviding more efficient operation. As such, the routine gradually rampsto the new desired ignition timing while gradually reducing airflow toaccount for the increased efficiency. In this way, it is possible tocommence an alternative fuel type during engine operation withoutviolating minimum pulse width requirements and thereby achieve improvedefficiency and maintaining engine output torque.

FIG. 40 shows an example of such operation where type 1 fuel is gasolineand type 2 fuel is ethanol or an ethanol blend. The top graph showsengine output torque (Tq), the second graph from the top shows theethanol pulsewidth, the third graph from the top shows the gasolinepulsewidth, the fourth graph from the top shows throttle position, thefifth graph from the top shows relative air-fuel ratio of the combustiongasses (λ), and the bottom graph shows spark angle. In this example, attime t1 the ethanol injector is activated to a minimum pulse width andthe gasoline injector is correspondingly decreased. Then, from t1 to t2,the spark is gradually ramped to a new optimal timing (which is moreadvanced due to the added charge cooling of the ethanol), while thethrottle is gradually ramped closed to compensate for the increasedefficiency of the engine due to the spark timing change.

In this example, fueling adjustments are shown for a fixed engine speedand load, and without delays from puddle dynamics, although compensationfor these may be added, if desired. Further, additional adjustments maybe present due to other transient conditions, such as feedback fromexhaust gas oxygen sensors, etc.

Referring now to FIG. 41, a routine is described for adjusting injectiontiming based on an amount of fuel types delivered to the enginecylinder. Further, the timing of delivery of more than one fuel type maybe varied (e.g., interval between start of injection of the types,interval between end of injection of the types, overlap of injection,the timing of one fuel type, etc.) in response to pressure in the intakemanifold of said engine, a time or number of cylinder events since thestart of said engine, an atmospheric condition surrounding said engine(e.g., barometric pressure, humidity, and ambient air temperature), atemperature of the fuel injected by said first injector or thetemperature of the fuel injected by said second injector, engine speed,engine load, coolant temperature, water fraction in the alcohol/waterblend, desired ethanol fraction, knock sensor indication, the durationof fuel injection for a first injector type or a second injector type,or combinations of these and/or other factors. For example, each or bothof an injection timing of a port injector and a direct injector for acommon cylinder may vary with these operating conditions to vary aninjection overlap, to vary vaporization, mixing, or others. As anotherexample, the duration between start of injection between two injectorsfor a common cylinder may vary depending on the amount of fluid deliveryby one or both of the injectors.

Specifically, in 4110 the routine reads operating conditions such asspeed, load, coolant temperature, valve and/or cam timing, airtemperature, humidity, barometric pressure, fuel temperature, etc. Then,in 4112, the routine reads a desired type 1 and type 2 desired fueldelivery amounts, and then selects the timings for type 1 and type 2fuel injection based on the conditions of 4110 and the amounts of 4112.Thus, as the conditions of 4110 change and/or the amount of fuel typesvary, injection timing of one or both fuel types may vary. As shownherein with regard to FIG. 42, various combinations of open valveinjection via a port fuel injector and closed valve injection of adirect injector may be used. Further, when only a single injectionsource is active, different injection timing may be used than when morethan one injection source is active. Further, the injection timings mayoverlap under some conditions and not overlap under other conditions.

FIG. 42 thus shows an example of port fuel injection of gasoline (or ablend thereof, cross-hatching from bottom left to upper right) anddirect injection of ethanol (or a blend thereof, cross-hatching fromupper left to bottom right). The top graph shows an example of closedvalve injection of port fuel and open valve injection of direct fuelduring an intake stroke. The next graph shows an example of both closedand open valve injection of port fuel and open valve injection of directfuel during an intake stroke, where the injections partially overlap.The next graph shows an example of both closed and both open and closedvalve injection of port fuel and open valve injection of direct fuelduring an intake stroke, where the injections do not overlap and thedirect fuel injection occurs at least partially during compression afterthe intake valve closes. Finally, the last graph shows an example ofclosed valve port injection and open valve injection of direct fuelduring an intake stroke, where the injections do not overlap and thedirect fuel injection occurs at least partially during compression afterthe intake valve closes. In the first three examples, the port fuel isgreater in timing than the direct fuel, where the opposite is true inthe last graph.

In one example, during idle conditions, open valve port injection may beused with a smaller amount of direct injection at least partially duringa compression stroke to improve combustion stability, such as during acold start.

Note that in one embodiment, two port fuel injectors may be used. Insuch a case, a routine similar to that of FIG. 41 may be used. In such acase, various combinations of open valve and closed valve injection viaone or more port fuel injectors may be used. For example, when only asingle injection source is active, different injection timing may beused than when more than one injection source is active. Further, theinjection timings may overlap under some conditions and not overlapunder other conditions.

One example approach for operating multiple port injectors is describedwith regard to FIG. 43, which shows a speed/load range with threeregions (region 1, region 2, and region 3), where region 1 is below thedashed line, region 2 is between the dashed and solid lines, and region3 is at or above the solid line. In one example, only a first fuel type(e.g., port gasoline injection) may be used in region 1 with closed, orpartially closed, valve injection timing. Further, a combination of bothinjection types may be used in region 2 (e.g., port gasoline injectionand ethanol injection, with each having closed and/or open valveinjection timing). Specifically, in region 2, as load increases, theamount of fuel types injected may vary, e.g., by increasing type 2injection and maintaining or decreasing type 1 injection. In onespecific example, the injections ramp to only type 2 injection at wideopen throttle conditions (the solid line, region 3) with open and/orclosed valve injection timing.

Referring now to FIG. 44, an example routine for controlling boosting(e.g., via a variable geometry turbocharger, electrically controlledsupercharger, adjustable compressor bypass valve, or a waste gate) isdescribed. Specifically, in 4410, the routine reads operatingconditions, such as engine speed, fluid reserve levels of fuel types(e.g., of gasoline in a first tank and ethanol in a second tank, orblends thereof), desired engine output, temperature, etc. Then, in 4412,the routine determines a desired boost amount (e.g., desired position ofa VGT, desired pressure ratio across a compressor, etc.). Then, theroutine determines a desired type 1 and type 2 fluid delivery in 4414.

In 4416, the routine determines whether a type 2 fluid reserve is belowa threshold value (for example, near empty, or the system is unable toprovide the amount desired in 4414). If so, the routine continues to4418 to reduce the boost amount to reduce a tendency of knock caused bylack of a desired amount of type 2 fluid, for example.

From 4418, or a no in 4416, the routine determines whether a knockindication is present in 4420, such as based on a knock sensor or otherapproach as noted herein. If so, the routine continues to 4422 todetermine if a first condition is present. For example, the conditionsmay be a high boost presence, a temperature is above a threshold, orother. If so, the routine continues to 4424 to further reduce a boostamount. Otherwise, the routine continues to 4426 to identify if a secondcondition is present. If so, the routine continues to 4428 to increase atype 2 fluid delivered and adjust a type 1 fluid if necessary to controlair-fuel ratio and/or engine torque. Otherwise, the routine continues to4430 to retard spark timing.

In this way, boost can be adjusted and engine improved engine operationcan be achieved under varying conditions.

It will be appreciated that the configurations, systems, and routinesdisclosed herein are exemplary in nature, and that these specificembodiments are not to be considered in a limiting sense, becausenumerous variations are possible. For example, the above approaches canbe applied to V-6, I-3, I-4, I-5, I-6, V-8, V-10, V-12, opposed 4, andother engine types.

As another example, engine 10 may be a variable displacement engine inwhich some cylinders (e.g., half) are deactivated by deactivating intakeand exhaust valves for those cylinders. In this way, improved fueleconomy may be achieved. However, as noted herein, in one exampleinjection using multiple types of fuel delivery (e.g., fuel compositionor delivery location) can be used to reduce a tendency of knock athigher loads. Thus, by operating with direct injection of a fuelcontaining alcohol (such as ethanol or an ethanol blend) during cylinderdeactivation operation, it may be possible to extend a range of cylinderdeactivation, thereby further improving fuel economy.

As will be appreciated by one of ordinary skill in the art, the specificroutines described herein in the flowcharts and the specification mayrepresent one or more of any number of processing strategies such asevent-driven, interrupt-driven, multi-tasking, multi-threading, and thelike. As such, various steps or functions illustrated may be performedin the sequence illustrated, in parallel, or in some cases omitted.Likewise, the order of processing is not necessarily required to achievethe features and advantages of the example embodiments of the inventiondescribed herein, but is provided for ease of illustration anddescription. Although not explicitly illustrated, one of ordinary skillin the art will recognize that one or more of the illustrated steps orfunctions may be repeatedly performed depending on the particularstrategy being used. Further, these figures graphically represent codeto be programmed into the computer readable storage medium in controller12. Further still, while the various routines may show a “start” and“end” block, the routines may be repeatedly performed in an iterativemanner, for example.

The subject matter of the present disclosure includes all novel andnonobvious combinations and subcombinations of the various systems andconfigurations, and other features, functions, and/or propertiesdisclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1. A method for an engine configured to deliver an actively varyingrelative ratio of a first and second fuel via a delivery system having afirst and second injector for a cylinder of the engine, the first fueldelivered by the first injector and the second fuel delivered by thesecond injector, where the first fuel has a lesser relative amount ofalcohol than the second fuel, the method comprising: varying an amountof injection from the first and second injector with operatingconditions; and when said variation causes said first injector toapproach a first minimum opening condition, increasing injection of saidsecond injector and disabling said first injector, and when saidvariation causes said second injector to approach a second minimumopening condition, avoiding further reduction of injection of saidsecond injector and decreasing injection of said first injector.
 2. Themethod of claim 1 wherein said first fuel injection includes gasolineand said second fuel includes ethanol.
 3. The method of claim 1 whereinsaid varying is performed in response to knock sensor feedback.
 4. Themethod of claim 1 wherein said varying is performed in response tooxygen sensor feedback.
 5. The method of claim 1 wherein said varying isperformed in response to engine speed or load changes.
 6. The method ofclaim 1 wherein said second injector is a direct injector.
 7. The methodof claim 1 further comprising boosting intake air entering the engine.8. A system for an engine, comprising: a fuel delivery system configuredto provide a varying relative ratio of a first and second fuel inresponse to a control signal, said provision via a delivery systemhaving a first and second injector for a cylinder of the engine, wherethe first fuel has a lesser relative amount of alcohol than the secondfuel, the first fuel delivered by the first injector and the second fueldelivered by the second injector; and a controller for varying an amountof injection from the first and second injector with operatingconditions, and when said variation causes said first injector toapproach a first minimum opening condition, increasing injection of saidsecond injector and disabling said first injector.
 9. The system ofclaim 8 wherein said first fuel includes gasoline and said second fuelincludes ethanol.
 10. The system of claim 8 wherein said varying isperformed in response to knock sensor feedback.
 11. The system of claim8 wherein said varying is performed in response to engine speed or loadchanges.
 12. The system of claim 8 wherein said second injector is adirect injector and the system further comprising further comprising aboosting device.
 13. A system for an engine, comprising: a fuel deliverysystem configured to provide a varying relative ratio of a first andsecond fuel in response to a control signal, said provision via adelivery system having a first and second injector for a cylinder of theengine, where the first fuel has a lesser relative amount of alcoholthan the second fuel, the first fuel delivered by the first injector andthe second fuel delivered by the second injector; and a controller forvarying an amount of injection from the first and second injector withoperating conditions, and when said variation causes said secondinjector to approach a second minimum opening condition, avoidingfurther reduction of said second injector and decreasing injection ofsaid first injector.
 14. The system of claim 13 wherein said first fuelincludes gasoline and said second fuel includes ethanol.
 15. The systemof claim 13 wherein said varying is performed in response to knocksensor feedback.
 16. The system of claim 13 wherein said varying isperformed in response to engine speed or load changes.
 17. The system ofclaim 13 wherein said second injector is a direct injector and thesystem further comprising further comprising a boosting device.
 18. Asystem for an engine, comprising: a fuel delivery system having a firstand a second fuel injector, each for a common cylinder of the engine;and a controller for varying an amount of injection from the first andsecond injector with operating conditions, and when said variationcauses one of said first and second injectors to approach a firstminimum opening condition, disabling said one of said first and secondinjectors and increasing injection of an other of said first and secondinjectors, and when said variation causes the other of said first andsecond injectors to approach a second minimum opening condition,avoiding further reduction of said other of said first and secondinjectors and decreasing injection of said one of said first and secondinjectors.
 19. The system of claim 18 wherein both injectors delivergasoline.
 20. The system of claim 19 where said first injector is adirect cylinder injector and said second injector is a port injector.